I've been to a few SLAs in recent years, and I've had to learn to identify a film that I can skip in order to get a proper meal in, because watching multiple films in one day is surprisingly tiring. There's also not a lot of places that stay open after the final film. For me, that's usually been a film in a franchise I haven't seen, but this year is trickier in that regard lol.
As for The Castle of Cagliostro, it was actually the very first Lupin III title that I watched. The franchise isn't very lore dependant, so you can just dip in.