1) I think a sturdy folder with a 3.5" blade and a 4.5"-5.5" fixed blade would technically be enough for me in most realistic situations, but I think I would put myself in the 3 is enough group. Short answer is 3.

2) A sturdy folder with 3"-3.5" blade would be used for most things, mostly out of convenience. A fixed blade with 3.5"-4.5" blade (preferably 4") would be used for bushcraft, hunting, food prep, all things that I would deem a little too much for the folder to handle. Finally, a fixed blade with at least a 7" blade to handle the heavy stuff like processing firewood and dispatching zombies (hahahahahaha!).

I have several knives in each category, but only because I haven't found the perfect knife yet. I have the designs in my head, I just need Dan and/or Jerry to make them. I will say that the custom shop Vex I have is just about the perfect knife for the small fixed blade role. For me anyway.