For the swap, does having 8GB of ram make a difference for the size of the partition?
From your statement about making mount point /, I assume that means Sabayon only needs 2 partitions (swap and root). This is how we've done it for Ubuntu at work so I'm comfortable with that.
1) Can Sabayon's installer do the partition table part? (and what is preferred by Sabayon/Linux?)
2) Can Sabayon live on an MBR formatted drive?
3) Would my UEFI BIOS care if I had a mix of MBR and GPT formatted drives?
this is like virgin helping a virgin..
(don't get me wrong, just installed my first sabayon earlier today) so i'll share some very fresh and probably very naive thoughts on the above.. hope that more relevant help is on its way..
the swap, as a general rule, should be twice the size of your ram.. however, i have for my setup made it eight gig for eight gig of ram.. from my experience, above the case where you have four ram and eight swap, it is unlikely to be put to good use if you allocate more.. but that's me.. i know people who have sixty and more gigs of swap who claim that they need it..
after a somewhat unsuccessful attempt to do a manual setup (it has objected that /boot and /boot/efi were needed (i usually only make three: /,/home,/swap)) i have handed it over to automatic, which went fine (use up free space, making some kind of a logical partition setup that i am yet to figure out how exactly is structured
don't know if all this may be misleading since my case is a little off (imac, dual boot with os x)..
as for your questions, my opinion, but no guarantees..
1) i'm pretty sure that it's a yes..
2) i really cannot see, even remotely, why it couldn't..
3) not sure on this one but, if i'd had to guess i'd go with, as far as my understanding of master boot record goes, it does not really effect the situation that you are describing..
best of luck..