Pretty tight but not over tight if that makes sense (e.g. don't jump on the allen key) if you give them to much force you can damage the taper on the crank. Locktite is always a good idea on square taper bolts
Just use a normal allen key and do it up as tight as you can by hand. Sometimes the bolts will stay in without locktite, sometimes they come loose so it's probably worth doing just to save hassle later on.