1: I don't like them either. Using unguided weaponry in such AD rich environment is IMO suicide. I use 2xKh-29L, 2xKh-25l, Vikhrs and AA-missiles. I used to load 2xS-25L instead of R-73 to maximize my AG performance, bu given their range they are probably not worth added weight.
2: If there are no radar guided SAMs you can fly higher than that. Point nose off the target to reduce closure rate, though this can cause vikhr to lose the beam, especially when firing at close range. Try to take out AD first, especially stingers. They are usually last vehicle in column.
3: Depends how much AD is left in the area. If there is strong AD presence, I usually do not fire more than one or two missiles per pass.
EDIT: To answer title question: Optimal attack range is maximum weapon range.
Also its important to destroy entire groups (columns, flights...) to score "result" points. For example, shooting down one A-10 and another one forcing to drop its stores and abort wont earn you any points.