How long would you expect an episode to be? And the length of the scenes also?
Me and another writer have completed the first episode of our sitcom at 51 pages long with 14 scenes.
Length
Read it out aloud. Allow pauses where needed. Best way.
If you're talking word counts then a Beeb length piece is usually 6-7000 words, but that obviously depends on a few factors. American stuff is usually 4-5000
The average length is usually 38 or just under. Well, that's what i've read. Oh, and for comedy films it's 90 or under.
I'd aim for under forty pages, especially if you're an unknown.