I can (sort of) answer no. 1 & 2:
Steady Aim all the way, all the attributes.
High Anchoring. IMO, you should invest at least 10 points in it. If you have 3x Centaur lv10 you may not need to max all the way.
Critical Shot got much better now. Not the highest single target damage, but definatly scales well with full dex and critical damage.
Time Bomb. I only see it used in pvp, and no more them 1 point.
Spiral Arrow is kind of okay against bosses, you need High Anchoring for better use of spiral arrow with the attribute Continuous Fire to be able to achive x5 the debuff on the enemy.
Bounce shot is okay for aoe set number, but you need the same attribute, Continuous Fire and aim well high anchoring to hit the most possible enemies so you can spam a lot.
If you deslike either bounce shot or spiral arrow, you may drop more points in critical shot or barrage if you want.
Barrage Shot vs Spiral Arrow: You can pull the combo with BS faster and in shorter time but need to get close for it. SA you can use at long distance but need a lot of time and use high anchoring with attribute for better use.
I honestly think Ranger 3 is going to suit SR right now. I don’t think you need both ranger3 and fletcher3 as fletcher3 is already good against bosses. May you reconsider ranger3 for scout? Cloaking to drop aggro on you. Even you decide go full str, wugushi at cricle 1 is not bad for bosses. Latent poison is very strong after 70 seconds.
As for cards, glass mole and rikaus might be userful for fletcher3 > mergen2