Ok I did one of these, so I'm an expert... OK at least I know how I would re-do it.
Is there insulation, vapor barrior in place?
I would use Tyvek as the vapor barrior, I didn't use one just blew in insulation, I get a lot of ceiling creaks... kinda like the house is going to fall down.
Yes paint or stain first.
If you have the time buy the T&G and then rick it and let shrink all it can. Bevel the ends if you are going more than one board length.
Stagger the joints, it looks beter if it is random.
Snap some chalk lines if you have a large ceiling, so when you get to the opposite wall you are even.
Hope this helps.
Rancher