your parents must be nice to let you have a 4ft tank!Im 16 and well wanted a 4ft tank but had to settle with only a 2 footer.In my other lil tank i had like only 3 of each(zebra danios,glowlights,neons,black neons and 2 swift rasboras plus a suckermouth catfish)and i can tell they want more of each other to play with so im getting 3 more of each so they total to 6 of each.The more the better im told.Serpae tetras are great too(getting some tomorrow)and they look interesting.But yeah there is a big range of fish to choose.Good luck in finding the ones you like.I find picking which ones to have to be the hardest.