If you don't mind getting your hands just a little dirty, I imagine this is very easily fixable, and very inexpensive to do so.
First, if you post your model number, I'm sure someone can chime in about being able to get the thing a little cooler. Usually there is a coarse adjustment screw (not easily found) on the thermostat that should allow you to drop your temp so that the actual fine adjustment knob that is easily accessible is useful to you in the temperature range that you want.
Second, beer line is very cheap. You should be able to replace a line for $3-$4 at the most. So if you can get to it, it would probably be worthwhile to replace it with longer lines if you're still having foam issues. The tower may make it really tough to get to if it's packed with insulation though, you'll have to get in there to see, or ask some other folks that have the same model - and certainly someone else on here does.
Lastly, 2.5 pounds isn't huge by any means, but should last quite a while and get you through quite a few kegs if you don't have any leaks (I use 20 oz paintball tanks - half of what you have - and get a couple of 5 gal kegs out of them easily). Once you decide how to go (replacing lines, adjusting temp, etc), I think you need to triple check that you don't have any leaks, all the way from the tank to the keg.
It's a bit of a hassle, but you can make your kegerator do what it's supposed to do. Try not to get too frustrated, it'll shake out eventually.