Flourite doesn't provide nutrients for the plants, with the possible exception of a little iron. If you have low light you can rely on the fish poop for the major nutrients, and the Flourite will be fine. But, with more light you will need to dose N, P, K for the plants to live.
Overdosing Excel can harm shrimp, but normal dosing should be alright - speaking of the hardy shrimp, like Cherry red shrimp. I'm not sure Crystal red shrimp could tolerate the Excel.