8-40 screws I use 18 in-lb with Loctite 272. Minimal Loctite, you don't want any to get between the action and the bases.
Depends on your goal. Personally I use green 680 Loctite between the base and action intentionally; it's a solid joint that'll never come loose until I want it to. Way too many accuracy issues and wandering zero issues are caused by loose bases and rings.
On the other hand if you're more concerned with the action finish under the bases, properly cured Loctite can be difficult to remove.