It's all up to you mate! I'm quite happy with what I'm running on the stock block. You might as well strap on what comes with the kit, and just turn it up to max boost. A built motor will take it no worries. Get used to driving that. It's quite a big difference! Probably good to run the motor in with tha too.
The adaptor is a bespoke part of the kit. You'll need something made up to link the manifolds, pipe to the ext gate, and the turbine housing, in a bigger, more free flowing design. It's not an off the shelf part!
Honestly, with a gt3582 think it would be pretty scary! But I'm a massive pussy. I like going round corners too, not just planting it In a straight line.