Not sure about question 1 (riflemen are very few and far between in the FIW)
In response, clarifying my question. In the stats for American riflemen, they hit on a roll of 4+ when shooting. Then, in the to-hit modifiers for shooting in the rules, a rifle gets a "+1 to hit" bonus.
My question, does the 4+ stat for riflemen already factor in the +1 to hit bonus given for a rifle, or is a rifleman's default 3+ to hit (before modifiers for range and cover, of course.
Also, thanks for clarifying the Firing Line rule.