My fishes need more friends. (30 gallon planted aquarium)?

I'm thinking of buy new fishes to add to my aquarium. But I'm not very sure what to buy.

I presently have:

3 filamet barbs
3 gold barbs
1 tiger barb
3 swordtails

I'm just thinking of buying 6 cardinal tetras.
what else could go nice?

please add fish that are not aggressive, easy to manage and fin nippers,as well as, type how many fish will I buy.

Thanks!