Are the chassan and kallah permitted to hold hands when coming into the hall after the yicud room?
There is no prohibition in doing so. Some prefer not to hold hands, in particular — but no only — among Chassidic communities, as part of the general custom of avoiding public demonstrations of physical contact. Many, however, make an exception to this rule for the chassan and kallah (for holding hands), and the practice has become customary for many. Some cite the Torah’s wording concerning Yitzchak, who “brought Rivka into the tent of his mother Sarah,” as a possible source for the custom.