Kudos go out to you for getting your cycle under control.
Yes adding established gravel and putting an established filter on your tank made quick work of your cycle time. In fact if anyone can get just a few cups of gravel from an established tank to add to their new tank it will shorten the cycle process significantly.
In fact when i started up my 29 gal
freshwater tank to take the fish from a friends 55 gal
tank that they had to tear down due to a moving situation I had no real oppertuinty to cycle the tank so I got a small tupperware bowl full of their gravel and placed it in the tank at the same time I moved their fish. I was given 5 2-3" congo tetras and a nice 4"+ pleco and two kuli loaches. I am proud to say my tank did not have any issues with ammoinia levels from day 1 and I attribute the bactera laden gravel from their tank as the reason.
I personaly Love a school of neon tetras. I cant get any for my 29 now as I worry the giant congo tetras (in compairson to the small size of the neons) would harrasse and kill them.