At only 20psi, you already have a decent looking intercooler. So charge temps shouldnt really be a problem even at 9.0:1. 10.0:1 is high and your engine will be knock limited and you will need something

So how the system is used will depend massively on that. I would advise using some of Aquamists new nozzles and do port injection. But sounds like you will only need a very small quantity of water.
And unless you are tuning and optimising timing as well, there probably isnt any point in bothering in the first place ( at least at 9.0:1 )
At 10.0:1 you will absolutely need some form of detonation suppressant.

Alcohol Injection Systems in the US make the neatest tank/pump system. I'd have bought that. The boost/progressive controllers are all pretty much the same. Nozzles vary in fitment, but are all pretty much the same except Aquamists. They are the smallest and neatest nozzles. But they have new ones with built in check valves specifically for port injection setups.

If the safeties are tuned properly, there is no reason why a problem with the water injection would pose any risks.