All alternate. There's no real watch order you need to stick to at this point, besides specific spinoff series (eg Fate/Kaleid Liner has 4 seasons and 2 movies which all need to be watched in order, but aren't affected by anything outside of them).

You can start straight with this one when it comes out if you want. Otherwise if you want recommendations for where to go next, check out Fata/Apocrypha, The Case Files of Lord El-Melloi II (yes that's fate, no I don't know why they dropped the Fate/ for that one), or diving your way into the eternal pit that is Fate/Grand Order, the Fate version of the Avengers movies.

Fate/Kaleid Liner Prisma Illya also gets shockingly good by the end, with some of my favourite scenes in the franchise, but you have to stomach through a lot of loli fanservice to get there, so your call.