Most fish store people don't know anything. I do say most because some like Blinky and others here work at fish stores and give their people the truth, and nothing but the truth. Well you have two problems here. One is our fish. They will all need schools, and some will need a bigger tank. The other is a cycle. Research the cycle. Search these forums for "cycling" and "fishy cycling" The cycle is a very important thing in fish keeping
1 serpae(sp?) tetra
Needs a school of 6
1 sword marigold
Never heard of
1 African dwarf frog
Perfect for a 10g
1 tigar barb
Very nippy and needs schools of 6. They may start to nip and eat you other fishes tails and fins
1 painted platy
Probably best keeped in schools of 4+, and it being pained means its been injected with dye.
1 pleco
Do you know what kind of Pleco it is?