The blanking plate should be made of something that isn't going to go soft at 700C. Mild steel is ok but prone to rust. Stainless steel (1mm thick or more) is better. Both sides should have Permatex Ultra Blue on the contact area.
Hard pipe all the way from turbo to intake is an interesting idea, and it'd be possible with a TMIC. I think FMICs are more popular but TMICs are technically superior (
here is a good read about the differences).
I wonder how much power you'd gain replacing the D40's FMIC with a fan-assisted TMIC, which would remove the heat from the cooling system ... interesting idea, but I doubt you'd recover the cost of doing it.