I suspect I'm the "well intended" individual you want to save him from but rest easy that I'm giving advice based on personal experience of small parts (not whole cars) rather than picking info from the air.
It generally is acrylic from Halford, the cans I have certainly are - as for "one stage" I'm not sure what you mean by that but it certainly works better when applied over primer and can be applied in multiple coats, that's the method they recommend. I consider that multi-stage but then I'm not in the business (I guess you are?) so am not up on the terminology.
My experience with it says it can be and very nicely to boot.
Would you like me to take some pictures of the 2500 4000 grit stuff I have? Or the 2000? I wet sanded my bonnet and intend to do a lot more, there isn't a chance I'd go near it with 1200 - 1500 though, 2000 followed by 4000, a couple of passes with a paint depth gauge backing me up.
G6! He wants to polish, not take the paint off and start again If you must use these god awful body repair products then maybe G10 but a nice Menzerna PO85RD 3.02 followed by some Final Finish PO85RD would be my preferred attack for a decent finish that isn't covered in swirls.
15 minutes if it's Halfords stuff, slightly longer in this weather I guess - I cheat and use a bit of heat though, the colour gets flatted back before the clear goes on anyway, there is nothing worse than a perfectly smooth clear over a crappy orange peel colour.
But other than this I totally agree with you and of course none of this matters if the prep work is pants.