The 1 inch rule is still used. Although I do agree that it's outdated and basing it on bioload/activity levels/ hiding places is a much better and more thorough method, but in the interest of keeping answer short and easy to comprehend, I figured more people would get the 1 inch visualization quicker.
I'm on my htc droid so, it is all done in my head....if the tank is 14g, I would plant it moderately so the fish can carve out their territories, leave enough room for your schools to play, and I would get corie catfish (i happen to love sterbai Cory cats...but whatever your taste!)...cories are great fish, playful, and they look like an intricate dance routine.
With your size tank, I would get at least 6 corie cats, since they will do better in a school.
Also, keep in mind that this stocking of the tank takes care of all 3 levels w/o overcrowding one level: bottom feeders, neons are mid water column, and betta at the top.
Just beware that your betta would probably dislike too rambunctious roomies as well as overcrowding and might begin to get violent.