Having just watched it I can say that you don't really need to have seen a lot of the MCU to understand what is going on in Far From Home. Of course you should watch Homecoming as you already have done as that sets up the characters for Spider-Man.
The film also deals with the fallout of Endgame as quite a major point. Therefore, to understand it you really need to watch Endgame and to understand Endgame you at least need to watch Infinity War.
You might also consider watching Civil War as that introduces the Peter/Tony relationship which is quite important for the events of Far From Home.
I also have an answer over on SFF where I discuss what one should watch before watching Endgame. However, if you're not too much of a fan of the rest of the MCU and only really want to watch the Spider-Man side of things I'd suggest just those 4 films are the core to get to grips with the story of Far From Home.
Far From Home does make a few references to the early Iron Man films which are quite nice and so would enhance your viewing but they're not really necessary. The most important ones are shown in flashbacks and the little details are more to do with how Peter is like Tony which are more subtle nods and clues.
I'd say you might want to at least watch Iron Man here as Far From Home does deal with
the death of Tony in Endgame
and understanding why that is so important at least starts in Iron Man. You'd also then pick up on more of the subtle nods I mentioned earlier.