5-0 is one of those fandoms that I've only seen two or three episodes of and still read fic of/try to write... So you really should be fine. But they'll be a good outsider POV on Javier and Kevin's relationship once the trilogy ends.

Claire's already had a few mentions for being the catalyst for exposing specials, and for being Bennet's daughter. She does make an appearance eventually, though. Sort of...

And yeah, Alexis should get some time in in part three, and she's going to show up in a few of the future!ludes.