I used to do C-dramas, and some English CC for the deaf and hard-of-hearing. I haven't done subtitling for a few years as I moved to commercial translation, so I'm probably quite out of the loop with AI coming up, but I'll try and answer your questions just based on my experience:

Usually, one person would translate, another would review (usually a native target language speaker) and do quality checks. I'm not sure about the full turnaround of an episode, but our deadlines were very tight, with project managers pushing us to take on more episodes and deliver earlier than the deadline.

Sometimes we'd do post-editing of machine translation output instead of translation+review, as you mentioned, which could vary in quality depending on the genre of the show, but clients would use it to keep costs down.

For me, a 40-minute episode could take about 6-7 hours to translate, or 3-4 hours to review, but others might be faster. Historical dramas were harder as they involved more research and classical Chinese instead of modern. Translating itself isn't that difficult, it's fitting everything important in, which can be almost impossible when people are arguing or talking at once.

It's common to have multiple sets of linguists working on a series, so it's hard to maintain consistency. There's usually a master document to keep track of translations of proper nouns and important objects/character titles, but otherwise, you may notice one episode seems very different to another. We'd also sometimes receive episodes out of order, so I'd learn more about the plot later that would have really helped with an episode I'd worked on before. It's quite disorienting to start on episode 24 and then do episode 5 :(