Wow, just had a read through the thread tonight. Terrific attention to detail. An E30 getting the TLC they require and some rather necessary modernization - will go very well.
Only suggestion I would make from personal experience is to NOT use exhaust heat wrap, the stuff traps moisture when cold encouraging rust, they also insulate the steel so well they get super hot, beyond what they normally would. I had a wrapped manifold make terrible contracting sounds because it was getting so hot, eventually once I took the wrap off after a while the stainless steel looked totally different as though it had been tortured excessive temperatures. I did some research and found a lot of horror stories of people using it and having rust holes develop over time, and particularly cracks. From what I understand, the only reason it exists is for motorsport and bike use where a mechanic or operator might burn themselves working near a hot pipe when they can't let it cool down, so it acts like a good safety feature.
In the end I made up custom manifolds and had them ceramic HPC coated inside and out, many years later they still looked exactly the same, no rust whatsoever.
If radiant heat is a concern a fabricated heat shield as well as HPC coating would be the best of both worlds.