It looks great and I admire your dedication to preserving the top growth of these plants for the few nights that they'll need it! Your climate is very similar to mine in North/North Central Florida.

The firebush will die back at just 32 degrees, but for sure will come back bigger and bigger. I've attached a photo of mine - it's two years old and was the same size as yours when I planted it. It died back about half-way even with a blanket and we only had one night of frost last year (32 deg. to be exact!). It didn't flower as profusely this year - the blooms are better on new wood, so you may want to consider letting it go, or cutting it back hard during the growing season. Mine is about 5 feet tall and wide now - but it does take FOREVER for the growth to fill out. It seemed mine didn't start putting out flowers and any height above two feet until June or July! I've been told that after a few years, as the shrub gets bigger and bigger, you'll only lose the tops of the plant during winter, and the dead leaves/stems will sort of "umbrella" the tender center and keep it from complete dieback. I wasn't prepared for the thing getting as huge as it already has, but I don't mind :)
I've compensated for the slow regrowth of the firebush/hamelia by planting some nice spring/early summer bulbs underneath of it. By the time it fills in and shades, the bulb foliage has already died back.

The Mandarin's will do just fine - they may lose their leaves, but they'll leaf back out. After a couple of years you shouldn't need to protect them at all. No fertilizers after August-ish; the trees need to start their dormancy in time for freezes. If you did fertilize after August you'll have new tip growths, that may survive, but it won't kill the tree if they don't.

The date palms are hit or miss - the tops where the new fronds/growth appear are the most important thing to keep from overly freezing. It might be a good idea to use some kind of white sheet and wrap the fronds, tie the sheet around the trunk securely, and then use the cylinders.

This of course all depends on the kind of winter we get. They'll vary every year. I find it gets cold enough for one or two nights to kill everything down to the ground, and then afterwards it's nice and warm. Be careful of surprise frosts that will pop up - It could be warm for an entire month and then overnight it will go back to freezing again.

If you can put some half-composted scraps down on top of the mulch the heat produced by composting can help add a couple of degrees. Pile on lots of leaves and needles, that helps tremendously. Another thing to try if you're not opposed is a smudge pot - a very old school oil lamp that burns and keeps the area a few degrees warmer. That's only practical (and safe) if it's sheltered from winds I suppose. The cold winds can be a real killer around here too.

Speaking of shelter from winds - a fence with vines, privacy fence, etc, will help shelter the plants from the killing...err..chilling, winds, if you can put one up. :) There's a few "pockets" or areas on our property where the air is very still in winter, and the tender stuff fares much, much better.

I think given what you've done that you'll have no problems this year with your plants - good luck and keep us posted - I look forward to seeing how everything fared by spring time! :)