I'm answering these in order of reading them so:
You can still use the washers for your windows! Most screenwashs contain up to 50% methanol anyway and majority of the rest is water! Screenwash just has soap and some colour! Methanol/alcohol will not damage your paint - scaremongering again. If it did I would have needed a respray by now! It doesnt even strip the wax protection off
You use a TB spacer which has the appropriate hole for a WMI nozzle holder
Space in the bay will be very limited, I doubt a decent size bottle would fit and you would be better off with a decent induction kit than WMI - I've seen the standard airbox cost 15-20hp at Stage 2+ - Get a VWR one if you want quiet but its foolish not having one.
£85 is the price for a decent product. No discounts and DO NOT get the CM one. It doesn't fit properly, comes with the wrong screws and ruins the spray pattern of the WMI injector - NOT AN OPTION (I learnt the hard way!). Either get the TB spacer from AKS or buy an aftermarket throttle pipe that has a boss welded on for the WMI.