+2 on the 20 long. That is a great tank to get back into the hobby with, just a great size overall for fish and for plants. I recommend shopping on this forum for plants as they are the best quality because they are from other fishtank people.
I would also recommend considering dirt(with a cap) in your tank. No co2, very limited/no ferts, and low to medium light. Check out "dustinsfishtanks" on youtube. Great growth (the dirt) with very little maintainance.
And lastly, I would consider ordering your fish from a website or possibly find a local breeder. Websites like wetspot, aquabid, live aquaria, or msjinkzd, a member on this forum that sells great fish. These fish easily beat the quality of almost all local petshops and it is worth it even though the shipping is a lot.
Good luck, and keep us posted!