Can give you my experiance on 2. And 3..

My second cog is a bit dicky on really cold mornings.. and sometimes if I'm trying to jump around gears a bit when it's warm. It's never really changed and hasn't given me any real grief.

If you're unsure of thier history best just to give the front bearings a clean and re-grease. They'll last for yonks as long as they've been well looked after. Any abnormal wear should be pretty apparent when looking at them.

The rear bearings are a "wet" bearing as far as I'm aware. Lubricated by the diff oil. My mechanic told me there's not much to be done with these. Apparently they'll last forever but big job if they do give up the ghost.