Here are some answers and some opinions:
From the JMT to VVR, it’s about 1-1/2 miles to the boat landing on Edison Lake. From here you can take the boat to VVR at the other end of the lake (runs twice a day, $18 round trip), or walk another 4.8 relatively shadefree miles.
I agree with you re the necessity of resupplying at VVR. Especially if you’re thru-hiking south, it doesn’t make any sense, because the carry from Reds to MTR is easy, and you’re going to want to load up at MTR for the stretch south of there. When I hiked, my friend and I did a resupply at Reds, then again at Muir Trail Ranch. We went off to VVR and spent a day there, but we did not resupply there. If I hiked again, would I go off to VVR? Probably not.
From the JMT over Kearsage Pass to the Onion Valley trailhead is about 7-1/2 miles, depending on which cutoff you use from the JMT to the pass. It’s roughly 2-1/2 miles from the JMT up to the pass, then 5 miles and roughly 2700 vertical feet down to the trailhead. From there it’s a 12-mile hitch down to Independence, which has groceries and a post office but is not a major resupply center like Bishop. The trailhead parking lot is pretty good-sized – I would guess 30 or 40 cars worth – so there would be some traffic in and out, but not a lot.
I can’t say whether going off here is worth it or not. When my friend and I hiked, another friend of ours carried in a resupply for the two of us over Kearsage Pass, then went the rest of the way with us to Whitney Portal. It wasn’t until this summer, when I hiked up from the Onion Valley trailhead over Kearsage Pass with a relatively full pack, that I realized how thankful I was that we had this option available to us.
How you handle any resupply south of Muir Trail Ranch is going to be one of the major decisions of your hike. A lot depends on how fast you’re hiking and how much time you have. If you decide you do need to resupply, and time is at a premium, you could always consider a packer resupply (see Wenk p. 238-9 for some names) but those are not cheap. Otherwise, unless you’re walking pretty fast and are willing to carry a heavy load out of MTR, you may be looking at a trip out.
Good luck!
Snobird