On things in a Series

Last week, my J-term one-act was read in my First Year Course (the course has to do with theater).  Having something I put effort into be read in normal circumstances is rather unnerving; I don't know whether I wanted to be excited or terrified about having people read this draft.  I'd actually put effort into it!  It had been revised more than once!  I didn't think it was atrocious, but it wasn't exactly the next Great American One-Act.
Anyway, the point of this is that one of the critiques I got from my theatre professor is that it felt like it could be a part of a series - that there were other things later on that could be learned.  While I agree with him on that point, I have no idea how I'm going to do that, or whether I should, and in what format I should do it in (stage play, screenplay, one-act, novel...).

Anyway, the point, I feel, of things in a series is that there has to be some overarching plot, unless they're the shows like 30 Rock or Big Bang Theory where the alternate title could just be The Misadventures of Sheldon and Liz Lemon.  If this thing continued into a series, it would have to be the sort of series that has continuity and an overarching sort of idea.  The thing is, though, I don't know if I have enough ideas for that, and every show - especially TV series - peters out sometime.  Take Glee, for example.  I mean, I haven't watched in a while, so I can't be sure, but it seems to have lost a lot of the long-term goals that it had at the start of the first season.  They haven't had any multi-part episodes that I recall since the first time they went to Regionals; even outside of the two-part Regionals bit, there were still allusions to the fact that it was looming on the horizon.  Late into the third season, though, it became more about the singing and dancing and the theme episodes than the overarching plot, though with some relationship drama.

At any rate, things in a series need to be sustainable.  You could write like Jon Flanagan (author of the Ranger's Apprentice series of ten books) and have plots span several books with continuity still between them - you can lump the first four books together, then books five through seven, then books eight through ten (I'm pretty sure my numbers are wrong on that, since I don't have my copies at school, but you get the general idea).

I don't know whether or not I'll write a series based on this one-act.  If I do, it won't be for a few months - I have novels to finish writing.

Anyway, what do you, fair readers, think of this?