if a team is 3 men down and there is a face off can all 3 attack men or dmen or combination come up to midfield?? take face off, stay on side etc.

Yes, as long as there are 3 men on each side of the center line. If one crosses to play the ball, it would then be offside. You have also prevented reentry from the bench area until possession is declared.

YES, BUT THEY MUST STAY ONSIDE. SEE 4-4.B

Two things to remember here:
1. When the faceoff man is one of the folks who "has to stay onsides during a man-down faceoff)" then when he goes down to do the faceoff and his gloves touch the midline (normally offsides) then the offsides rules is waived for that FOGO man until he is finished the faceoff.
2. In Fed. rules, if that near wing is left open, then the man coming in from his penalty can enter field when his pen. time expires. In NCAA, he must wait until possession is called, or ball goes into def. box or goes out of bounds, etc.