The water is very dependent on the port where they restock. We had three different brands of premium water on our South American cruise - one batch from Buenos Aires, one from Ushuaia, and one from Valparaiso.
There are multiple socket types in the cabin - 110v two-prong and 220v European plugs. I always bring adapters simply because there aren't anough outlets if you restrict yourself to one type.
In Luminae, we tend to tip everyone whether they've served us or not. They work as a team and in our view, just because they don't carry the food to you doesn't mean they deserve it any less.
We got some food service disposable gloves from Amazon and use them whenever we use the buffet. You can also ask the staff for a pair if you don't have your own.
Not in my experience. I generally put in $300-$400, play no more than $5, and repeat the next day. I believe it's ship-dependent, as I've heard there may be issues on the newer and revolutionized ships.
Wow. We were on the Infinity for 24 days in March and had a wonderful experience. Yes, we had problems with the closets and our refrigerators didn't work (we had it replaced multiple times), but found the staff in Luminae to be great. The only problem we had was on the very last day where they overcooked both my steak and eggs at breakfast. I can't comment on the other venues you described since we never visited any of them.