Crazy idea, thoughts and opinions?

So I have a 2ft CS currently in a horizontal 40-gal breeder (36x18x16"), I've always wanted to turn the enclosure in to a live tank, and that would be fairly simple if I didn't want to do something crazy.
So here's the general gist of the idea, I turn the tank on its side, creating a vertical (36" tall) tank featuring a waterfall flowing into an aquarium section at the bottom, with three levels of dry space for my snake to explore, and about 15" of water for him to enjoy as well.
To do this I would remove the now top panel (18x16" piece) and place it at the bottom, creating a small 19ish gal tank at the bottom and leaving the top half enclosed by mesh screen. Here's a rough idea of what that would look like.. Naturally the three levels will each feature a hide as well, mostly hidden under the waterfall structure on the left side.
I have some concerns and want to make sure my design is solid before building it, mainly I want to know what might be the best heating design as I fear top down standard lights would not reach the bottom of the tank, in addition I'm concerned that the levels may not offer enough space for my snake to sprawl out on (is it necessary to have horizontal space, or can vertical space substitute?)
I also want to make sure my selected plants won't be toxic to him, and that any fish or cleaners don't attack or affect him (currently thinking guppies and isopods/springtails) and these plants: Dwarf schefflera, Orchids, Pothos, Parva plant (aqua), Thyrsiflora (succ), Pinguicula (succ), earth stars plant?, Peperomia, Ponytail palms, Sansevieria trifasciata.

Any advice or criticism is welcome!

https://imgur.com/a/cOQ4I89 looks like my image link didnt work

The glass used for the bottom pane of aquariums is different from the glass used for the side panes. The bottom pane is stronger and designed to withstand the pressure of holding the weight of all the water. I don't know if the depth of water that you're looking at will create enough force to break your glass but it would be an obvious weak point in your design.

The general rule for housing snakes is that the length + width of enclosure = length of the snake. An 18" x 16" footprint doesn't seem large enough for an adult cornsnake, especially with water and waterfall areas sucking up floor space.

I would expect standard heating lamps to provide adequate heat in the setup. You could also get a thermostatic-controlled aquarium heater (plastic ones made for turtles, perhaps) and set the water temperature to 75 F or so. A volume of warm water at the bottom of the enclosure is likely to help overall temperatures and a basking light might knock down the humidity enough to avoid fungus and whatnot.

Plants aren't generally an issue for snakes, at least as far as toxicity goes. Most toxic plants that are commonly kept as house plants are only toxic if ingested and your snake won't ingest any plants. Assuming you feed frozen/thawed, the prey won't eat the plants and pass along toxins either. You'll just need to watch out for plants that excrete toxins, like the desert rose, whose sap is an irritant (if my memory serves me correctly).

Springtails and isopods are fine, I keep them in with my cornsnakes. I spot clean, the bugs take care of the rest.

I would not stock any fish. Your snake is going to produce an enormous bio load without any help from fish. Freshwater shrimp would be a better choice assuming your water temperature doesn't get too high. Lightly stocking the water, adding an aquatic plant or two, and letting pothos root in the water will allow you to just run an air pump powered sponge filter, a rather low maintenance yet effective approach.

You may be better served by keeping your tank in its current configuration and building a tall, secure top to house your waterfall and other landscaping. I once had a frog tank where the base was a 10 gallon aquarium and I used plexiglass, wood, and screen to build a 10 gallon extension above it. If you use that approach then, if you decide that the water is way too much maintenance, you can convert everything back to the 40 breeder in an afternoon.

I’d stay away from water features and waterfalls with corn snakes. While they benefit from moderate humidity the high humidity from water features may be detrimental.

I don’t do bio active for my snakes, but I do for my gecko. I really like Josh’s Frogs for a source of reptile safe plants, substrate and CUC. I’ve also heard good things about NE Herp though I have no personal experience with them.