Answer to "doesn't respond after water damage"At this point if your iPhone is recognised by the computer but no screen output: first things first, I'd get the board cleaned in a ultrasonic cleaner (do not for the love of god use rice!) the reason for this is, even though you've used Isopropyl Alcohol thats not agitated the crap and oxidation to come off the board. Then try a new screen, if thats still a bust then i'd move onto possible board repair. May have blown the Display IC chip. I've recently changed a Touch IC chip on an iPhone 6 after water damage. worked like a charm.
Answer to "Turning on device without wifi antenna installed?"Should be fine, what you'll find is that WiFi connectivity will be limited or just greyed out in settings.