My Wastegate runs off my manifold, but I'm going to tap the compressor housing and put it on there. Running it off the manifold won't create a laggier spool, it only means that the signal going to the wastegate is lagged. This means that you CAN have spiking or oscillation issues with your boost pressure. However, with such a large turbo like yours, it won't really matter that much. It will probably work fine. If you DO have spiking issues, then move it. Some cars run this way stock (like old Volvo Turbos) They had mad spike issues because of it, but they ran a pretty small T3.
As for the ISCV, I just left mine open (Actually, I stuck a cork in it with a small hole drilled in it, as my ISCV doesn't work)