Saturday, May 4 is Star Wars Day (“May the Fourth be with you”). It is always impossible to predict crowds and we don’t know what Disney will do that day (usually special merch, photo ops, character stuff), but it may well be amped up with all the SW hype - I’d be cautious about that particular Saturday.
My perspective on Mondays is that they’re more crowded than people
expect, but not usually that out of line with the days surrounding them. We go on a lot of Mondays. Heck, I was at
Disneyland last Monday and am going again at noon today. They’re usually significantly more crowded than, say, Wednesdays, but there are occasional weeks where that isn’t even true. Over the summer, I’d say most Saturdays are definitely less crowded than most Mondays due to AP blackouts and a high percentage of tourists trying to “avoid Saturday,” but it’s not that cut and dried the rest of the year, ESPECIALLY with the ticket deals.
I mean, it’s not like Monday is going to have this MASSIVE spike in crowds compared to those other days. It might be the most crowded of those four days (it also might not be), but it’s not like you’re going to have this dramatic, horrible experience on Monday that wouldn’t occur on Sunday or Tuesday.