a leaking water heater did this stain on the ceiling...see pic. Can i try paint, spray or something? what is this ceiling tile called? Is it hard and expensive to replace? My best option to make it look better on a budget? Thanks

So, I have a ceiling to redo. It was popcorn from the 80s, no asbestos. It had been partially scraped as in no high spots, but some areas are rough, some are smooth. And it looks to have been painted/primed over, after left smooth/rough. The rough areas would be about 1mm thick, I don't think any are as thick as 2mm, however. Also, there do not appear to be any issues with damage or tape coming off. I've been thinking about the best way to go over this. A few thoughts I have had were to 1) go over it with a thicker skimcoat to even everything out, then apply either some sort of roll-on, or stomp. Those seem like they would be slightly thicker to hide any imperfections that may linger after the thick skim. 2) sand the rough spots a little more to make them a bit more uniform, then texture. 3) sand all the rough stuff off, or sand it a bit, then wet it to remove the rest and get things really smooth. So, that is the first area I have questions. Second would be about the texture itself. What should I use? How should I mix it up? I've seen mixing j/c with point. Some seem to talk just about using j/c. I have done 1 ceiling, it was smooth, and I just mixed in a sand texture into the paint and it seemed to work well. 3rd, texture types. I am leaning toward either a stomp of some sort, or roll-on. I'm not sure I want to try and learn how to work a hopper gun. So, what type of texture would be easiest, with less (hopefully) mess, that would cover well? Now, I have seen knockdown, and that looks like it would cover well; but you roll it on, then smooth it with a knockdown roller. My question on that is how much pressure do I apply to the knockdown roller? Nothing seems to address that. As I said, a barrage of questions! Hopefully, this wasn't all too jumbled!