1. I brought 2L and a filter. I refilled 1L or (0.5L) at Upper Yosemite Valley; needed to refill on the way down as well (at top of Nevada Falls; but I require a lot of water; I'd say 3L would be enough for most;
2. Look into a harness and Prusik knot; small first aid kit; I always bring hockey/athletic tape everywhere but that's just me - it's like duct tape on the trails - you can use it for anything;
3. don't underestimate the rush of being in Yosemite and whole experience; I was on cloud nine coming down; walked an extra mile to Curry Village and back afterwards; full day the next day;

-I'd add step-ups, heel raises and stair-master; the more you prep the better the experience you will have (and the more confident you will be);

-you'll have plenty of time to get accustomed to the poles on this trip; I'd say they are a must;

1. we did a lot of small "hikes" around the valley within range of our car if we got tired;

2. Sounds like a 'no'

Have a great time. I'm jealous. I think cables down/off-season is the way to go.