Why 3m?  Power kites are generally made in sizes from 1.5m to 21m.  You want something that will be easy to learn on, still provide some decent pull but won't completely wear you out.  Something around the 3m mark is usually ideal for the average weight person.   For a start, you don't want to be fighting a kite while you're learning to fly it.  You want to be concentrating on flying it and having fun, not survival.  For most of us in the 65 - 85kg range, the 3m size is ideal.  Big enough to provide a fair bit of pull in 10 - 15 knots and powerful enough to buggy with should you go that way.  Plus, smaller kites in the 2m - 3m range are fairly quick through the sky and a little more exciting imho than the bigger kites.  4m - 5m kites start getting noticeably slower and it's a bit like hanging on to a truck - a lot of effort and you'd soon wear yourself out - depending on the wind strength.  Bigger sizes can produce more power in lighter winds, but if there's not enough wind for the 3m to fly then it's more than likely you'd struggle to fly a 4m or 5m.    Even though a 2 - 3m power kite is relatively small, don't underestimate the power that they can generate if flown in winds beyond what you can handle - they can hurt so stick to lightish winds while you're learning.

Why 4 line handles?  4 line handles (a pair of power lines each side of the kite and a pair of brake lines) give you the most versatility.  You can easily reverse launch the kite should you land upside down.  You can also bring the kite to a complete stop by pulling the brakes and when you are learning, you'll quite likely have some velcro bands around your wrist with a line attached to the brake lines of the kite.  These are called 'kite killers'.   You just let the handles GO and the brake lines will be pulled killing all the power in the kite.  See pic from Peter Lynn below...

4 line handles are also compact, easy to store, provide the most control for your kite and are relatively inexpensive.  2 line kites tend to be a bit difficult to relaunch from an inverted position and harder to land. 4 line kites may take an hour or so extra to initially get the hang of than a 2 line kite, but the extra hour will pay big dividends.  

Low aspect?  Beginner kites are normally 'short and fat'.  These are low aspect kites.  High aspect kites are long and thin - lots of extra performance and speed/power but demand much more skill to fly. They are usually designed as high performance 'engines' for buggies.  Leave them for later.  While low aspect kites are often labelled as 'beginner' kites, they are not something that you will necessarily outgrow - they are often characterized by having excellent stability - particularly in gusty wind - and having very good manners.  They are excellent kites for days when the wind is less than ideal.  If you're not chasing that extra speed in the buggy or trying to go that extra 15% upwind then there's no particular reason you need to upgrade.

Ok then, which kite?  Stick with a known and respected brand like Peter Lynn, Ozone, PKD, Zebra, HQ, Born Kite, Flexifoil.  All these manufacturers make excellent quality kites that should last for years if not crashed too much.  Good kites to buy first up are the HQ Beamer, the Peter Lynn Hornet, Flexifoil Rage, Flexifoil Sting, PKD Buster, Zebra Checka, Zebra Z1 and Ozone Quattro.  There is also the single skin Nasa Star 3 from Born Kite that is an excellent kite to learn on.  The best thing you can do is ask lots of questions on a forum such as this.  Better still, get together with some local flyers - you can learn far more in an afternoon flying with other people than any other way.  In the meantime, there's always youtube videos...

Once you've got the reflexes working and you can fly your kite without needing to look at it, then you might like to get into some 'traction' kiting - ie: snow kiting, skates, landboard, or my favorite mode of transport, the buggy...

You're standing on the bank of a fast moving stream.  In the center the stream is fast and smooth.  It slows down as it nears the bank due to friction with the land.  Any obstacles, rocks, trees etc disturb the flow of the water and the water will often be flowing in the reverse direction as it goes around and eddies back in behind the obstacle...

If there's a lot of obstacles, it can be a quite a chaotic mess.  Now, pick the whole stream up and stand it on it's edge and you have a pretty fair picture of how the wind interacts with the land.  Buildings, trees, hills etc will all affect the flow of the wind the same as the water in the stream.  You need to get up and away from them to find the smoother air higher up.  But with power kites, we don't have the luxury of letting out 150 meters of line to get the kite above the disturbances so we have to examine our surroundings.  Buildings, trees and undulations will affect the wind a lot further than you think - you need to be as far downwind away from them as you can.  When I was in my early 20's I used to build and fly stunt kites but I didn't know much about how the wind was affected by it's surroundings.  If there was wind, great, I could fly in the local park....so I thought.  It cost me a few smashed stunt kites to slowly work out it was all the trees and buildings that were the problem.

But it's not just getting away from obstacles that we need to think about as inland kiters - thermals can make a bit of a mess out of the wind too.  A thermal happens when the sun heats up a particular section of land - maybe it's on the side of a hill facing the sun, maybe it's a plowed paddock that's a little darker...or a car park, road, building etc.  As the land/carpark/building warms up, it, in turn heats the air above it.  At some point a warm 'bubble' of air gets heated enough to rise up from the ground - becoming a thermal.  Ever watched a lava lamp?

Thermals in action!   And when that bubble of warm air breaks free of the ground and rises - cooler surrounding air has to rush in and fill the void.  Thermals are great for glider pilots (or birds!) as you can gain height for free by flying round and round in them - some are large and some are narrow and some can be a bit violent.  For a land kiter, it all adds more variability into the wind.   You might think you're in a clear location and the wind is relatively smooth, but if there's thermals going off around you, you may suddenly find serious shifts in both wind speed and direction.   Sometimes your best chance of smooth wind is an overcast day where the sun is not creating yet more havoc.

Sometimes thermal activity may be obvious by all the cumulus clouds building around you, but rising air doesn't always result in a cloud being formed...

So, don't choose a spot surrounded by trees to fly.  Or buildings.  Get into a clear an area as possible.  If it's a little elevated, better still.  Truganina is a good spot in Melbourne - it's elevated and mostly clear of trees.  While it still can be pretty turbulent and gusty, it's pretty good for an inland spot.  If the wind is coming off the bay, better still.

The best wind for kiters is the afternoon seabreeze.  The sun heats the land and towards the end of the day, the air over the land begins to rise and the cooler air over the sea rushes in - it can be quite sudden.  I've been at Kingston where I was barely flying in 6 knots and then within 5 minutes, the seabreeze of 20 knots came in.  The seabreeze can be really smooth with very little variation and flying in it is an absolute joy.  The kite stays nailed to the sky and you'll feel far more in control.  That's why we will travel long distances to get, not only the smoother wind coming in from the ocean (or bay), but also the large expanse of hard sand the low tide exposes.  

Temperature of the air will affect your kiting too.  I've had good sessions with a 6m Ozone Access in 12 - 13 knots - a wind speed that would normally be a bit low for that kite, but it was a cold dense wind.  The same wind speed in Queensland (for example) would be a lot warmer and less dense and hence I'd probably need at least the next kite size up.

If I'm contemplating a kiting session at home, I will give the trees a good look - if they're bent over in the wind, but otherwise not moving about much, that's great.  It means a consistent wind.  If they are waving wildly back an forth, not so good, that means lots of gusts and lulls.  And I hate it when you're flying a foil in gusty wind and there's a big lull, the kite promptly folds up in a ball and begins to fall out of the sky and back in to the middle of the window only to be hit by the next gust, then unfurl in the middle of the window and go POW!!  "I'm back now"! and tries it's best to rip me out of the buggy.  Sometimes the wind is so gusty and messed up, that it's just not worth the risk in flying.  And sometimes it's smooth and a joy.  Learning to pick the right conditions takes a bit of time and observation but will repay with you safer and more enjoyable flying conditions