Some suggestions:
On the gears... While you're getting used to the bike, put the front into the middle chainring, and just LEAVE it there, and get used to working with the back wheel 7 (or 9?) gears. That should give you the middle 75% of the available gearing on the bike, without causing any problems. You really only have 12 or 13 real gears anyway.
To educate yourself further, read THIS
http://sheldonbrown.com/gears.html Then read THIS
http://sheldonbrown.com/gain.html Try to pedal in as low of a gear as possible, keeping your pedal RPMs up in the 60-80 range. That will help keep excess stress off of your knee joint -- and also give you more power. It's a lot easier to climb an incline pedaling fast than pedaling slow. When you're more confident on the bike, THEN work on front/rear gear combinations...
Regarding the 16" front wheel -- relax your steering grip. I've got an EZ-1. It's GOING to wobble, with that small of a front wheel, but it's also going to be very easy to correct a wobble. And U-turning (or turning in general) gets easier the more you learn to lean into the turn. ESPECIALLY relax your steering (and shoulders) when going slow -- you'll find the bike will steer itself.
While you're riding, keep two fingers on the brakes at all times. Since you're just essentially resting your hands on the tops of the grips, it's no big deal to just lay your fingers across the brake handles. That way, they're there when you need 'em!!!!
Keep us posted on your progress! And DRINK WATER...