Got these today at my local greenhouse for $3.50, how can I ensure healthy plants, a large yield, and spicy peppers ?

3 ghost pepper plants and 1 Carolina reaper.

1st picture all four plants
2nd picture top of ghost pepper plant
3rd picture top of reaper
4th picture closeup of large 1” ghost pepper

I’ve read I need to plant them in pots at least 12” in diameter: I currently have 4 10” thin plastic ones I got at the greenhouse for free. I plan to put them in those since I have nothing that large and pots that large (that are also decent) are expensive.

I’ve also read I need a more acidic soil. I currently have a big bag miracle grow garden mix and some sand leftover from this spring. I have a place they can get at least 8 hours of direct sun a day but I’m scared of scalding them, since I think they might end up getting much more. I’ve been told there are certain ways to trim buds and stems so that the peppers grow in better. Are these plants too mature for that?

Any advice to the care of these is super appreciated.

I know it’s late in the season but I really want to get the best yield I can out of these plants as a first time super hot grower. Thanks all!