I am considering either going over Agnew Pass to exit at Silver Lake, or Reds Meadow via the River Trail or High Trail. Any options from those who have hiked this section? I should add that I plan to spend as much time fly fishing as possible, so that may affect your answer.
Also, any input on the best camping spots and where/where not campfires are allowed along the route?
I had to look up the Agnew Pass route you mentioned. It like a looks shorter exit. But when I was in there, friends left from Garnet Lake and were at Agnew Meadows in about 4 hours. I and a friend took the JMT, and by hurrying, came out at Reds Meadow in about 5 hours.
But the two things I would definitely recommend:
1. Camping at Thousand Island Lake. It is one of the prettiest places on the JMT.
And 2. The trail used to go from Island Pass straight down to the lake. I have the Topo! maps that show it. But you won't find that trail, and instead it turns eastward and descends several miles to the outlet of T.I. Lake. If you go, I would definitely recommend leaving the trail and descending to the lake. The old trail most likely took off where the current trail makes the abrupt left turn to the east. If you go this way, you will arrive at the lake at a far more unused part, with good camping & fishing options. And there is a nice path along the shoreline (the old trail), so you would not have any trouble heading out that way.
The center of this map shows where I'd leave the trail and head south-southeast to the lake: