Geezer here, concerning tickler/triggers. Usually I make my ticklers from 3/8 in. (9mm) square mild steel bar. I usually flatten the forward end a bit where the trigger bolt goes thru, to give me more steel on both sides of the bolt-package, and it usually ends up a bit less than 3/8 from the top bend forward, and narrower still (perhaps 7 mm) at the distal end (fits into the sear-keyway) The tickler's tail is usually either rat-tailed, or flattened into a spoon. Period medieval bows, which were usually stronger than mine often have thicker trigger/tickler thru the center... as much as a half-inch (12mm) square, tapered at the head and tail. As for slack, I don't intentionally put slack into the trigger passage, but usually there's plenty of space. If the trigger is too loose in the passage, I'll shim it out with leather pads.
As for trigger springs: I suspect plenty of medieval crossbows were entirely springless. I have made a few that way, but generally my customers expect a trigger spring, so I include them. Geezer.