Are you asking about where you should place the H9 in your pedal chain? That depends partly on what sort of algorithms you want to run on it. You might want to put pitch effects at the front of the chain whereas reverbs would normally go at the end. The H9 has a pre post function where you can use its two inputs and outputs to place it at two different positions in your chain as well.
There aren’t any limits on algorithm purchases with the H9. There’s enough space on your Core to hold all of the algorithms at once.