I got my first BP about a month ago and went with similar choices as you're considering.

With branches, you can get your own depending on where you live. Look up what species are safe to use (I used apple), and pick branches on the tree that are dead but not rotted. You then want to trim off any pointy ends and excessive branches, strip off any bark, then smooth the whole thing down with sandpaper. Next, put them in the oven at 250 degrees Fahrenheit for two hours to kill any microbes in the wood, wash afterwards and they're ready for use.

As for hides I'm using those half logs. He seems to like them just fine and they'll provide a rough surface for when he needs to shed, plus they come in two sizes so when he gets bigger I can simply switch to the other ones.

Not sure about the plexiglass as I went with a screen lid and utilized cardboard wrapped in aluminum foil to serve as humidity guards (though they aren't working as well as I'd like). My best suggestion would be to drill a hole for the lamp so the heat isn't directly on the glass, and fasten a screen over the hole to prevent escapes. I also perched mine atop an empty mike stand and put a clamp on the wire to keep it from slipping off.

Jumpstart thermostats work perfectly fine for my setup, so you're good there.

I use a Zoo Med thermometer/humidity gauge as it comes with dual probes, though be aware if you use this you'll want to hot glue the wires in key places as the snake will all too easily move them around and mess up the readings. Same for the probe you'll use for the CHE (remember that it will need its own thermostat).

Generally wouldn't recommend aquarium decor. They tend to be too craggy and sharp and can have potential spaces and holes where the snake can get stuck (the fake skull and castle ones are notorious for this). A safe bet is some fake plants from a craft store. Just make sure they don't have glitter or the like on them or have exposed wire and that they're sufficiently washed before use. Bundles of fake ivy are a good example.