really, your neons, cories, cherry barbs and all the tetras should be in groups of 6+. this however would overstock you i reckon, and certainly wouldnt look very nice. before putting any other new types of fish in, i woudl strongly suggest sorting out those problems first. tanks almost always looks better with 1 or 2 larger shoals of fish, rather than with all the different species you have. trust me, i made the same mistake, and am now regretting it. fish act so much more natural when in decent sized groups, and it makes for a much better tank. once my current stock thin out, im going to stick to just one type of tetra and cherry barbs. it will look so much better.
if i was you i would swap the harlequin, lemon and rummynose tetras, platties and the cherry barbs for more cories, neons and black skirts. at a push i would keep a small group of cherry barbs, cos i think they're mint. but those other tetras really have to go.
10 cories
6 black skirt
fighter
bn plec
ram
10 neons
10 cherry barbs
saying that, im not a fan of the black skirt tetra, so wouldnt have them at all. but seen as you almost have a good number of them, might aswell keep them.
