1. If you disable secure boot to be able to run Linux will Windows 8 still boot?
Yes.
2. If Windows 8 will boot will it play protected content while secure boot is disabled
It will.
3. If you do not disable secure boot, but instead insert your own key will that erase secure key storage by default and thus remove Microsoft's key?
Depends on your firmware implementation - some systems only let you install keys by removing all the existing keys. However, you can enrol as many keys as you want to while you're doing that, so you can add your own key *and* Microsoft's key.
4. How complicated is to sign Linux kernel which you have compiled?
Trivial. You just need to use sbsigntool or pesign.
5. How does secure boot affect projects like linux from scratch, Hirens Boot CD, etc?
You'd really have to ask their developers what they think the best approach is.
no subject
Yes.
It will.
Depends on your firmware implementation - some systems only let you install keys by removing all the existing keys. However, you can enrol as many keys as you want to while you're doing that, so you can add your own key *and* Microsoft's key.
Trivial. You just need to use sbsigntool or pesign.
You'd really have to ask their developers what they think the best approach is.