Hey Foley,
Don't lose heart mate. It sounds to me like you've tried to do way too much too soon.
For your next build you need to buy it (obviously), plan what colours you need and sort them and make sure you have all the tools you need also stuff like putty and a pin vice helps for drilling out barrels helps too.
I assume you, like most of us, are on a tight budget so keep things simple. When it comes to the upper hull that's easy as you can get to that any time to paint. I like to leave tracks and wheels off until the end to paint and weather separately as it's very hard to paint them well on a pre assembled model (imo).
I'd recommend a Tamiya kit - something in 1/35 scale is perfect. The StuG III is a good little kit for starting out on. Also, look at the Panzer III or Cromwell. All can be painted in a single colour so no need to worry about cammo yet!
As for using other models to base your builds on and to take initiative from that's fine as long as they are built well (again, imo) but nothing beats the real thing if you can find some good pictures etc. Buy some DVD's etc to see the real things and you'll see how the crews really did hang stowage on the tanks. othing beats good research - these guys have taught me that!
Best of luck!
All the best,
Ben