If I just want to make the simplest roasted cauliflower, what is the best temperature and roasting time?
I have never roasted it, only boiled and fried it before.
There's a lot of range of acceptable outcomes for this, so let me give you the parameters I work with.
I generally start by mixing the cauliflower with some oil (olive oil typically; others substituted depending on the flavor profile I want) on a baking sheet, then sprinkling with salt. This part is important; if you skip the oil, you'll likely just end up with dried out cauliflower. So every other bit of guidance I give is based on that. Additionally, it's important to try to spread out the cauliflower so that it makes just a single layer.
350F works well when I don't want to pay much attention while roasting. It usually takes 30-60 minutes, depending on how finely I break the florets. Larger pieces take longer. I usually check it every 15 minutes or so and flip pieces around. In most cases, you'll get more gentle browning with this temperature than with higher temperatures. You'll probably get the softest, sweetest cauliflower this way.
If you are more impatient but you are willing to check on the cauliflower more frequently, you can easily go up to 425F. I can shave off a fair amount of time, and I've had good results with even large pieces cooking fairly quickly, often in the 25-40 minute range. The caveat is browning is much more aggressive, and you need to rotate pieces more frequently, possibly every 8-10 minutes. You will often get a more caramelized result than with lower temperatures, and you may find cooking slightly less even. I sometimes prefer this because I like a balance of chewy and soft texture and I like the extra caramelization on the surface.
Generally seasonings other than salt are best added near the end of the cooking process so that you don't burn them; spices, herbs, and garlic in particular can't typically handle much more than about 15 minutes baking.