You got things rollin
1st.. I have a 30 long 48"x12"x12" i use for quarantine and its great.. I have Duraplex Plexiglass from lowes over the screened lid. The reason I say Dura Plex is because when you lift a 48" long lid it bends and flexes, if you get the cheap plexi it will snap.. This was $19.99 for like 42" and I got it cut to (2) peices so a RHP can sit ontop of one side (Hot side) and the Plexi fits 11" wide inside the metal frame. I drilled 4 holes im the Plexi (dont push let drill work) and put small small bolts and nuts threw the screen hole.. Make sure holes are 1" in or it cam split the Plexi. It works perfect.. After all your not throwing the lid around anyway. Instead of a RHP ($100) you can leave 1/3 open for a CHE.. Which you also asked about. A CHE will last longer, is more efficient, and I don't like to worry about Night/Day lights ect.. The snakes prefur dark anyways... As far as lights to see, id go with a LED strip.. You can use Hot glue (I use DAP bath & kitchen Silicone).
The LED are what most of us are ordering in our PVC enclosures. They look good and its better to only use them when you want to look at your snake or clean.. As they rather not have a spot light on them of course.
Last the Probe.. You want the probe on the glass and you want the substrate paper thin in the Hot spot so your measuring the hottest part of glass and snake is getting the full 88-91 basking temp..
i used Silicone also for the probe and over the wire in a couple places to keep it from being pulled. Let it dry for 3-4 hours (use a good amount to hold the probe and wire) so the smell is gone.. Spray some glass cleaner and it will help with the smell after it dries...
I think i touched all your questions.