I'm by no means an expert only have had mine for a short time. He is in a 40b, I went with a small one about 1.5-2". Have plenty of liverock for them to pick at. Also I feed fresh then frozen clam,mussle and oyster mix and he devours it. He also likes that Hikari angel food mixed with pe mysis. He is in a LPS dominated tank.
From what I read the smaller ones usually do better then larger ones when first introduced. Have plenty of liverock for them to graze on. I didn't qt mine but a lot of people recommend getting them eating and fattened up in qt. I also read once you get them eating and comfortable they are fairly hardy and easy to care for like other Angels. A lot of people in the past reported mystery deaths after a year or so.
In my 28 Jbj I have a cherub angel that doesn't nip on any SPS or my clam, I also have a flameback in a fowlr and he is also very easy to take care of. All 3 of them are model citizens and do not bother corals, fish or inverts. I love angel fish and eventually I would love to have a very large tank and have some of the big Angels. They are my favorite species of fish.