For plants, the best source really is this forum, great deals on here usually and really nice selection of plants.
But some other places are BamaPlants and HanAquatics.
As for filtration, the one SunSun 304/404 (pretty sure this is what you got) is technically enough filtration. An additional AC70 doesnt hurt, neither does another one, but it is a bit unnecessary. But over filtering doesnt hurt as long as the current is tolerable[censored]for the fish. If you overstock, then by all means do use extra filtration (I probably overstock the most on this forum).