A few suggestions.

It can be really hot in July in the valley. If it is 100+ degrees in the flat lands, it is going to be in the 90's in Yosemite Valley. The valley gets crowded and full of air pollution in the mid-summer. I personally avoid the valley in the summer. Spring and Fall are the best time to go to the Valley.

The worst mosquitoes I have ever experienced was on July 4th in northern Yosemite at about 9,000-10,000 feet elevation.

The John Muir Trail is really crowded. Mid-week is better timing than weekends. There are lots of nice trails that get less use. Also, even if you are on a heavily used trail, you can always have privacy at camp by staying away from the standard campsites. Walk a quarter to half a mile off trail and you will have it all to yourself. Take two Platypus 2.5-liter water bottles so you can have the option of camping a bit away from water (thus away from the crowds).

Little Yosemite Valley is an ugly, over-used, crowded campground plagued by ill-behaved bears. There are many nice spots to set up a tent before you get there. Nothing says you have to stay at the back-country campgrounds. Just be at least 200 feet away from the trail and water. It is not legal to camp between Little Yosemite Valley and the trailhead at Happy Isles.

If you do a one-way Tolumne to the Valley, you have to get back to your car. I believe you have to pay about $20 or so to take a bus back. You may consider looping back to your car by a different trail.

Yosemite trails are good for a first solo trip. The junctions are well signed and the country is distinctive so map reading is easy.

From Nevada Falls, the Mist Trail is much more spectacular than the John Muir Trail. Do not believe those who say the Mist Trail is not good for backpacking. I backpack up and down this trail all the time - you just have to go up and down a lot of rock steps. Take it slow and enjoy the views! Trekking poles help.

The backpacker's campground in the Valley is really nice. You are allowed to stay there the night that you come out. It is $5 per person.

Have a great trip!