A master's SOP runs 800–1,200 words and connects three things: your academic foundation, the specific gap this programme fills, and what you will do with it. Naming faculty and modules is what proves you researched the department rather than the ranking.
Usually 800 to 1,200 words, or one to two pages, unless the university states otherwise. Follow their limit exactly — exceeding it is a common and avoidable rejection reason.
An SOP is academic and forward-looking: your research interests and goals. A personal statement, especially in UK applications, allows more personal narrative and motivation.
For master's and PhD applications, yes. It is the clearest evidence that you chose the department rather than the ranking — but only name people whose work you have actually read.