Class A uniform in a wedding ?

For technical purposes, you would wear the uniform the same as if you were attending a similar military event. If you're in an airborne unit, then yes wear jump boots. SPC Joseph Wojcik answered the head gear question. As future reference, most events done in the military in the evening time don't wear head gear inside or out.

If the wedding is indoors, don't wear headgear.
I'm not sure about the jump boots, read AR 670-1.