Glenn you are awesome. (Glenn's our resident angel and you're not alone in benefitting from his generosity.)
But I don't think you need to spend $400 bucks on a sleeping bag for this trip. I agree, that this is where you want to step up and do better than a $20 Wal-Mart Coleman bag, but top of the line stuff isn't the only way to go. It is the lightest and best way to go, but there are lot's of people that have done Yosemite without $400 down bags. Probably more than not.
I use a Coleman eXponent 32º backpacking bag, with a Coleman fleece bag liner, wear good long undies (top and bottoms), a wool sweater, fleece pajama pants, fleece hat and gloves. I use a bubble foil pad on top of my sleeping pad, and a SOL emergency blanket over my bag, and I am warm and cozy down to 20º. All of this together cost less than $150 brand new, and it weighs considerably more than a Western Mountaineering UltraLite bag
The take away should be that you have options, but you need to attain the same end result no matter what you choose. You must be warm at least to 20º.
Topo map skills will be essential. You haven't mentioned how well you know how to use a map and compass, and South Florida doesn't offer much topography to practice on, but you do need to have or hone those skills for this trip.
You should download all the topos for Yosemite (they're free at http://libremap.org
), and start studying them. Get to know them as best as you can and cross reference them with photos so you can better associate what is on the map with what you see.
Follow the major valleys, note the peaks and gaps, and the mouths of creeks and cuts coming down from the ridges into the bottoms, and try and familiarize yourself with the terrain you'll encounter. Try to learn what peaks you will see from wherever you are, and how they will come into view as you travel. It's reassuring to find the features you expect while hiking along the way, and it's the only certain way to know where you are.
You need to be able to visualize the shape of mountains as displayed on the topo map and recognize them when you're looking at them for real, and from all angles. If you can do that, triangulating your position on a map is easy as pie in the mountains.
I use topo maps to help me with planning my route. I look at them and visualize the area, and find places that I want to explore. For me, that's usually the valleys and creeks and cuts. Others here prefer the peaks and ridges, or both.
I guess what I am searching for on a map is the perfect place to spend a night or two. A flat spot where two creeks come together, or a waterfall nearby. You can find where they are likely to be on a topo map if you visualize what they display and it's a wonderful way to escape for a bit and relax and dream. Out there you have mountain lakes that are just stunningly beautiful to plan a night at.
For all I know, you've been doing this for years, but if not, get those maps and get lost in them. Shoot, you've got Google Earth to help you visualize the area. When I was your age all we had was..... (ah well, I'll spare you