I am a decorator, not a lawyer.... if a customer asked me to provide a higher quality of finish, I would quote to line the walls. Materials aside, you are looking at about 8/10 hours of labour per small/medium room. The problem however is that he didn't do that when initially quoting. I cannot comment on why he didn't.
If I see excessive orange peel build up on the walls, I will recommend lining paper. If it is slight (and not vinyl silk- which gums up when sanded),I will simply sand the walls. .
I have no way of knowing how much he contributed to the orange peel effect.
A few years ago, my other half used a checka type site to find a decorator to paint our hallway- she didn't want to wait for me to be free.
The day that he finished, she paid him, and asked me to repaint it (in the same colours). I had to sand away his emulsion build up- I had previously lined the walls and only applied two different coats of paint prior to him messing up the walls. Previously, there was no noticeable paint build up.
The paint felt as though there was grit in it. I suspect that, given it was a very hot week, he applied a second thick coat too quickly. All of the woodwork had grit in it as well. Recifying his work added about 30-40% extra labour.
From your posts, you have explained that you were happy to pay a premium for a high quality finish. From the (selected) images that you have posted, you did not receive a high quality of finish. In my opinion he should have recommended lining the walls, given that you stated that you wanted a better quality of finish.
Any small claims judge will expect you to offer him the possibility of rectifying things before litigating. If you are asking him to line the walls, he will then have to repaint the walls and cut in the woodwork and ceilings. That will have a massive impact on his pocket. He could reasonably insist that you pay for the paper and his labour to line the walls (and possibly for the paint). He can also argue that he thought that he was providing the quality of finish that you were happy to pay for.
It could get messy, very messy.
Before going down that path, perhaps keep nagging him to improve things, or to refund you a sizable amount so that you can get someone else in. In all likelihood, both of you will end up out of pocket though.
Sorry, I wish I could be of more help- either way though, get a minimum of 3 (detailed quotes).