I wouldn’t reccomend wasting bonus points on spirit, focus on strength and power. You may also need to add some dex if you are missing a lot, but some items can add dex (like the bazooka M9) which allows you to focus your points in strength and power. Necklaces will provide spirit for skills although sometimes it might be a few levels past the level you are supposed to unlock the skill in which you can wear a necklace that gives you enough spirit to do so.
It really depends on what weapon you are using. If you have an M9 then i would recommend 10 base dex. If you are using a gun appropriate to your level, i’d say 500 is fine at 150. At 350 you get Concentration which raises your hit percentage by like 90% or so which allows you to cut out dex, so don’t add too much unless you plan on resetting.
TBH if you aren’t using an M9 I’d suggest trying to get one. It makes life a whole lot easier for a canon.