Well... to start with I promised /aco/ I would, but didn't because I was too tired, so I felt I had an obligation to make good on my promise.
To go back a little further, I had a basic concept after reading a TS! thread here on /co/; several Anons had pointed out that Britney seemed to have a crush on Alex, which seemed entirely plausible to me. Lots of people do lesbian shipping for this show, but usually with all three girls, which never quite seemed in-character for me; let's be honest, who can see CLOVER being lesbian for anyone?
So, I had a seed for an idea, which led me to remember the end of an Alex-centric episode which seemed to have a good "lead" for such sapphic shenanigans, without anyone acting too ooc. The only research I had to do involved checking the TS! wiki, so most of the hard work had already been done for me. I'll still have to take some liberties with canon if I want to make the sequel I've got in my head, but I'll cross that bridge if I come to it.
As for pacing, you just have to ask yourself: "How much set-up would *I* want to read before getting to the good stuff?". Of course, you have to balance that out by asking "How much will the reader want to sit through before getting bored?"
Think about good porno studios, like Sweetheart Videos - they spend a fair amount of time before getting to sweet lesbian sexy times, but they do it by setting up characters and what their motivations are. That makes you care about the characters getting it on, because it's emotionally fulfilling to see them getting what they want. This continues when you see the porn stars interacting with each other in a natural, yet obviously erotic way.
Now, look at the shit-ton of crappy pornos - they either use boring camera shots of fucking nothing to pretend they're "artsy", or they just have characters boning on flimsy pretexts, with barely any interaction besides grunting and yelling generic "sexy" things - e.g. YOU MAKE ME COME SO BAD - ad nauseum