The bigger the better! Really, 29g is still considered a nano but you'll be able to keep lots more stuff and have more stable parameters. The only thing that's really going to be the budget factor between a 5 gallon and a 29 gallon is the lights. It's a lot more expensive to light a 29g for corals than a 5g. Craigslist would be your friend, though.
Good luck! The best learning is through trial and error and I hope it's not an expensive learning experience! lol
Good luck! The best learning is through trial and error and I hope it's not an expensive learning experience! lol