As it turns out, my wife and I moved here from O'ahu.
On my build I scrapped the fenders and then also the chain guard. I couldn't get the fenders to stay straight so I pulled them off. Then I couldn't get the chain guard to stop rattling, so I pulled that off also. The other issues you're going to run into will be the 48 spoke wheels and the oversized tubes. These can be over come but it'll take some experimenting to get it right. That's why I went with the friction drive. It's not cheap, but it works. Pretty much a no brainer.
If you get a lot of rain must mean you're on the windward side? To be honest, I don't think that would be a major issue, but as we haven't had rain in over a month I can't say for sure.
Good luck with the traffic on O'ahu. I've been hit by a car there and have witnessed lots of accidents. Probably one of the most dangerous places to ride a bike IMO.