When I started out, I had a lil 12ga, which wasn't my wisest of choices... Nitrates built up on me and constantly stayed at 40ppm. That lil tank was some good luck though, cause nothing died in it (None of my 3 fish, 2 corals and 1 blood shrimp), unlike my 90ga that I recently got. Been having so many problems with it...
Money wise, I would go with a smaller tank, 12-29ga. For just a regular starting tank, 30-65ga. If you've got extra cash, go 75ga+
The bigger the better, because the chemicals(amm, Trite, triate) will spread slower, giving you time (Unlike small tanks), and you get a wider variety of fish. The only thing with big tanks is that they are expensive, I've allready spent about $1,000+ on mine.(90ga)
If you get a small tank, I just have to say;
skimmer,skimmer,skimmer. Will save you from
ammonia build up.
If you get a bigger tank, go with a natural filtration. You could buy or make a
sump, put sand on the bottom, build up one portion of it with A LOT of rock rubble, as much as you can, and in another portion, put
chaeto with a PC or T5 light over it. This is GREAT filtration for when ammonia starts buildng up. A skimmer cannot be your only filtration, wont take out all fish poo, so there will be ammonia.
I never had experince with the natural filtration, but I'm switching to it soon. Right now I personally have a skimmer, some filter pads, and bioballs.
I hope this is usefull!