It also helps with some bikes to fill the system, then rock the bike back and forth to free up bubbles. Almost every engine has some nook or cranny that's hard to fill, and some have lots of 'em!
As far as the coolant, every bike manual I have read -- and that's maybe a dozen -- specifies 50/50 water/ethylene glycol antifreeze. Several are specific enough to state never use only water or only antifreeze, but I am sure in a contingency where you lacked one or the other you wouldn't hurt anything short-term. 100% of either is better than not enough!