Novella in between books one and two?

Okay, I'm officially bonkers. I just had the idea to write a novella (might as well call it fanfiction for my own book series) set between the first and second books. There is a 1.5-year time gap between these books, and I often wondered what the characters did during this time. I briefly touch on it at the beginning of the second book, but wouldn't it be nice, actually, to flesh out a few scenes? To show what occurred to make the characters change and develop further. I've already sketched five scenes, alternating between POV's (as I do in my main books). And one bittersweet ending...

I don't want to make it an official part of the series (you don't have to read it to follow along with the narrative), but I'd like to include it as a nice little extra.

After I finish reading my proofread copy of my first book, this might be the perfect time to start working on this novella. Lengthwise, I'd like to keep it reasonably short, no more than 25k -30k words. What do you think?