Okay, still, this is way more in-depth than the approach i'd foreseen. I had only three scenario's in mind, not evaluating patch by patch. Unless you're volunteering
1. Vanilla source from kernel.org + grsec patch applied ( as is the recommended approach )
2. Distro source ( vanilla + distro patches ) + grsec patch ( throws a warning/error because it is not vanilla source )
3. Vanilla source + grsec patch + distro patches ( untested and as you suggest most likely food for n00b frustrations )
Anyway, i now know as much as when i posted the question. Thank's anyway i did pick up a little along the way.