I really like both of these ideas! As far as the Brian and Nick story goes, I'd like to see pre- and post- Leighanne stories (I know you dislike her greatly, but I think she's such a big part of the history of their friendship). Maybe a one-shot around the shooting of the ALAYLM video (1997?), and perhaps something on Brian's wedding day (that was September 2002 I'm pretty sure). I'm a big researcher into the dates in my stories, so I feel ya.
As far as the Howie/Kevin/Nick one (I am so excited about this one! Sorry Brian and AJ, but these three are my faves, and it can change daily between the three of them), my ideal story here would be present-day action/adventure with a lot of bromance, too. Though, you kind of already went there with Hope. I'd be up for a straight-up bromance, too. Hot mess Nick could also be fun, though. Maybe delve into his relationships with Kevin and Howie during this period. Hot mess Nick spans a lot of years, though- so you have a big time period to work with there.