Saxman, How would I tune this though with just a piggyback?

At this stage I think I will leave the intake manifold as is due to money constraints (just found out I need to pay for some custom rod bolts). I will run the 5mm oversize TB I already have on it, and at a later stage maybe once I get a better ECU I will upgrade the intake manifold

Assuming I have a full standalone ECU, what kind of gains will a ITB setup give me?