Would this combination of factors make sense?
You know, the answer here is "idk maybe ?". Making sense is itself kinda hard to pin down since your description is super vague. You could look at all the individual factors and see what those depend on. For instance, you want low clouds. Ok, a top level guess would be the heavier a cloud the lower it sits. Indeed, you can go as low as ground level. Its call fog. As such i would guess, for low clouds you need you know probably a lot of water vapor.
Would someone human-like survive the radiation in the higher, thinner atmosphere of a mountain top?
Probably ? I mean people survive in the antarctic provided they have a habitat. So if you can sling load a shielded habitat up there people can probably survive. But this depends on other factors. Like... is there a magnetosphere ?
Or would a cloud layer here be burned away?
By what ?
Perhaps the tallest trees would be graduated from darker at the bottom to lightest at the top,
That is a question of evolution. Which has very little to do with "reason" and more with what happens to work, and what happens to work. While science disagrees, my personal conspiracy theory as to why plants are green and not red is because a billion years ago there was Alice the red algae and bob the green alga. And then Oh no ! Alice got crushed by a random rock hence why all plants are green.
While this is hyperbolic, it is also kinda true. Evolution is a game of luck. And often times very dumb solutions just work. Look at your own body. Half the stuff could be improved by a 5yo.
So when it comes to evolution and how stuff looks, while there are general guidelines, its all kind of ad hoc. That being said, dark leaves probably make little sense. One theory why plants are green has to do with heat management.
Would the sky still be blue/white? What color would sunset be?
May i interduce you to a great tool, known as Spectral absorption diagrams. The color of the sky, depends on the composition of the atmosphere. If you have a lot more Vapor in the air, it will be foggy.
Generally speaking, whenever you have a different atmospheric composition, just google a spectral diagram of the gas in question. For instance, lets say an atmosphere has more O2. Well then this graph can help us; 
This tells us, oxygen absorbs predominantly red wavelengths. So if you have more oxygen, the sky will be bluer. But again, this is a super general statement. irl it depends on more but just saying "Boi this sky is bluer" works.
What would be the effects of a longer day, i.e. 30 hours?
That is a very broad question.
What would the tide be like on a planet that's technically a moon for a gas giant? It is a fair distance from the giant.
I dont think anyone can answer this. Tides are more complex than most people imagine. The best you will get, without simulations, is "They exist".
or maybe just the sun's intensity is higher so most creatures retreat until evening. Does this make sense?
Not really.
artefexian
I dont want to be a hater or anything, but all of this is speculation. In the sense, when you really dive into topics (especially this many) the answer will always be "We dont know how this would work". Its fine to invest time into all of this, but it is just not an exact science. Sure, in general we can say the weather does this, mountains for like that etc. But in specific cases these rules basically always break down or have giant * attached to them. So many factors play a roll, you just cant account for all of them.
