Nice!
Actually I think what you have there is a 29! I LOVE my 29 gallon tanks, it is a great size.
Definitely check it well for holding water...in a bathtub or outside if you can.
Your equipment for the 10 might work on a 29 but you might want to think about upgrading the filter depending on the size you have now. You should be sure on the measurements first...and then you can go from there
Do you have a stand for it?? If not, you should be able to find one at a garage sale or on craigslist pretty easily.
Oh, and in a bigger tank I would definitely go for a bigger school of both your harlequins and the neons! With that mix you could get most any calm community fish for a centerpiece... Just be careful if you switch filters that you don't go into a mini-cycle...be sure to transfer everything to the new tank.