>>528558794
Thing is usually those new Fate/Spin-Offs stray off from FSN at some point so you are good enough there. Newer works tend to reference FGO in some shape or form with parallel versions of the cast from there and vice versa, but Strange Fake happens in a FSN-like timeline ala Case Files.
The one that has to pay attention a lot to FGO is, well, Narita (SF's writer) because his ideas for his HGW took too long, so when FGO's roster got expanded, a lot of the developments there were stuff Narita himsefl wanted to explore and this causes him to rewrite the story over and over again and again. For example: one of the servants is related to the Count of Monte Cristo. In FGO, Edmond Dantes is a full blown servant so Narita cried that there was too much of an overlap and he'd have to start preparing excuses.
It's kind of an issue in the opposite side of the spectrum from Fate/Apocrypha; Apocrypha underused its cast and rushed the war. Strange Fake develops its cast so much they are like, 3 days in the war even now. An hour that passes inside Strange Fake is an hour you witness through the narration of multiple servants/masters. If Gilgamesh is doing X, the narration will show Enkidu doing Y and then the Police will do Z, and then it shows Zealot etc.

So, FGO will give you some context, but you aren't in a rush there to understand SF. As long as you did FSN you are set.