Q1 as to which distro others probably have more experience than me, but a lot of peeps seem happy with leo4all.
Q2 Before you try anything else I would try removing memory and going down to 2 gig.
I'm using intel and i have no crashes, that doesn't mean its definatly your processor but eliminate the memory first. I think that might still be your main problem
Q3 Best way to update, read threads on here and do what has worked for others.
Q4 Easy BCD

Hope this helps