Are air fryers difficult to master
It helps if you're a proficient cook already, know what foods cook at what temperature and a meat thermometer helps too, for frozen sausages and similar.
I have got a basic Tefal that came with hardly any instructions, their app recipes didn't list any of the foods I wanted to cook.
I think if you buy a more upmarket model it will come with more detailed instructions.
can you put plastic containers in them
Like
@ColinJ said, this is a very bad idea
If you want to heat/cook ready meals, you must decant them in a metal (oven) dish.
I use an old baking tin that fits my air fryer's basket.
living alone would a small one meet my needs?
Yes if you cook only for yourself and if you eat small portions.
I live by myself but have 2 full sized ovens, a micro, a hob, an air fryer and a slow cooker

Today I cooked for the cats and I processed a load of vegetables that I got for free - I share food with friends.
So I used the slow cooker, the hob and one of the full sized ovens
It sounds like I still need a microwave, more than I need an air fryer! How about one of those microwaves that act like a conventional oven in browning and making food crisp, if required?🤔 Having a microwave AND an air fryer would be difficult due to a lack of space in my pokey kitchen!
I have never owned one, but those kind of microwaves seem to be suitable.
If your kitchen is small, you could get a small kitchen trolley on wheels for extra worktop space, when you need an appliance you can just move it from the trolley to near a socket on the worktop.