First of all, I feel for you and I hope the damage is not too bad.
I can`t answer all the questions, but I`ll try my best:
1. I would assume that unbrunt oil passing through the exhaust will burn in the headers.
2. Depends on the size of the metal particles. Best is to see what you get caught in the oil grid when you remove the oil sump plate cover.
3. I am not expert enough, but I assume piston-cylinder are junk at the very least.
4.
Here is a recent e-bay example for $1250. I say they can be had for relatively cheap because they are not as desirable as the 3.0L alu blocks.
5. You are in the right place to get all the help you need !
Good luck!
Aurel