At what point is a man allowed to touch a woman that he has just married. Can they touch after he has placed the ring on her finger and said "harei at..." before the 7 blessings are completed? Are they allowed to hold hands on the way to the yichud room? Can they touch after having yichud even if the marriage has not yet been consummated?
Shulchan Aruch (EH 20:1) rules that it is biblically forbidden to receive pleasure from bodily contact with anyone who is an Ervah (ie. forbidden to marry).
So, if the bride is a Niddah, than no one may receive pleasure from bodily contact with her. If the bride is not a Niddah, than until she accepts the ring anyone in the room can receive pleasure from bodily contact with her. Once she accepts the ring, she becomes Erva (אשת איש) to everyone aside from the groom and thus everyone else is forbidden to receive pleasure from bodily contact with her, while the groom is not.
Independent of this biblical prohibition, there are general issues of Tzniut/Hirhur (avoiding licentious thoughts) which have to be adhered to always by all (see for example EH 21).