Is it glass or screen?
If you're looking at Phelsuma, that tank would nicely house a pair of grandis! They make awesome display animals, and don't require you to go searching for them everytime you want to see them.
Have you thought of Anolis sp.? A pair of Anolis equestris ssp. would do well in that tank. They are not the most docile animals (though from your post it doesn't look like you were wanting to handle them anyways), but they are amazing display animals. The only "downside" (subjectively) is that they'd detroy smaller, more delicate plants, and they'd eat literally anything that will fit in their mouth; including fish.
I'f you're wanting a water section big enough for fish, I'd skip any terrestrial species and stick to arboreals. Not because they'll drown (unlikely unless it's an act of aggression like stated above), it just takes up space that would be better used as foraging space for the animals.
55x45x90cm (Is this an Exo-terra?) isn't a huge tank, so I'd stay away from mixing. This is for a few reasons;
1. Novel Pathogens. Especially if mixing species from different areas. You risk passing on parasites/bacteria/viruses that one species may not be accustomed to, and in turn kills it. Being captive-bred limits this risk, but doesn't eliminate it. Let alone the chance of the pathogen mutating and jumping to a new host. There are many examples of this happening:
-Chytrid likely being spread globally from the distribution of Xenopus spp.
-Mycoplasma infections in Gopherus sp. from South American tortoises
-Monkey pox spreading from pouched rats to prairie dogs to humans
-Herpes B from macaques to humans
-Rats spreading numerous human diseases
2. Unless they are coming from the exact same habitat, they are going to require diferent environments. Even if they are both rainforest species, one may prefer the slightly drier and less stagnant air of the canopy, while they other may prefer the dark, humid, relatively stale conditions of the forest floor. You can replicate this to some degree in tanks, but not really all that well without compromising somewhere.
3. Aggression/feeding. Will the animals compete for food? will one want to eat the other? Will the food of one bother the other?
4. Space. That tank may be ~230L (~60gallons), but since it isn't filled with water, and these aren't fish, they aren't using all of it. They are only using what they can get to in the way of branches, plants, &c.
5. Stress. Are there visual barriers that allow the animals to hide to their own liking? Not just from other species, but from each other. Will one of the species stress the other from striking at it or chasing it?
6. This links back to #4 & #5. How is the tank setup? Is it better suited to one species over the other? Are the plants able to be used as hiding spots, perches, &c.? Don't bend the species to the tank.
I'm not saying it can't be done; many have. But just because some have done it, doesn't mean it's a good idea. I'd suggest extensive experience with any species before even thinking about mixing them.
Mixing reptiles is a whole different ball game from mixing fish (though the same problems are found in both).
I may have extensive knowledge of fish, especially Channa, I am an uter neophyte when it comes to reptiles, so your post, while some don't like people "teaching" them stuff, is a gold mine and I thank you for it!
As a channa lover, I am quite acuainted to sacrificing entire tanks to just one specie, and even just two fish, so the concept isn't bothering me too much, I was just thinking of adding some diversity in colors. Was mainly thinking of dendrobates and some small gecko, but if it is indeed a problem, I won't go through with the idea, which means I have to find the perfect species for this thing.
I am not sure of what an exo terra is, but mine is basically a tank with assembled panes extending it upwards, with 2 sliding doors on the front. So the bottom is leak proof, the top, not so much.
Will try to answer some points with what I had in mind, since I don't have the knowledge:
2. I'll post a pic of what I'd like, I was still trying to figure out how to make it look good as i'm terrible at DYI backgrounds, but I found out Xaxim is a thing, which would make my life a whole lot easier! I basically intend to have rain dropping from the pump through a pierced bendable pipe in a spiral, either continually, or X times a day (if it's noisy, i'll have to keep to that, but it'll be running a month prior to introduction of anything, as I assume both scenarios don't allow for the same species).
3. As forementioned, was hoping for dendrobates and small geckos, still a bad idea? Nothing that comes out as compatible? I don't really need to have the whole thing crawling with critters, but diversity is nice (though I have that with just dendrobates I guess).
4. Picture at the bottom for this one too. That is what I want, and since I would like water at the bottom, I'm aiming for as much usable places up in the air (branches, small platforms, long leaved plants, etc) to avoid repeating the mistake I did with my chameleon that basically sat in one place because he didn't have much other choices.
5. Same logic as fish, so I would probably have thought of hiding places, or at the very least, things that break line of sight. Nothing worse than a bullied animal letting itself die... in the best case scenario.
6. Explained in 5, and it's still in my head, I have the terra, but it is still empty. I'm still trying to figure out decoration, so I am still able to bend the tank to the species rather than the opposite.
I do get your point though, same goes with channas where everyone saw videos of a guy that kept them with other fish, so they all think it's doable, but we rarely see the same guy posting 6 months later.
Thanks a lot for taking the time, by the way. Learning is probably my favorite part of the hobby (be it fish or scaly critters), and passing on knowledge when it is acquired is a close second.
Here's what I found that looks like what I want (except mine will be taller so I assume darker at the bottom):
