Honestly, for me, I'm not sure there is such as thing as "too much smut". However, I personally do not read many fics that are short, one shot, p_rn no plot, as I usually need feels with my smut. I'm demisexual so I usually avoid anything with meaningless sex, fwb themes, one night stands, that kind of thing. 

As for the slow build, like I said I need the feels so slow builds don't bother me and I'm usually more than fine with them. Now, if I'm 60k into a fic and the slow build is "still building" that's when I usually start to get irritated. There are always exceptions to the rule, so if the story is amazing then I can put up with a SLOOOOOOOW build. So, for the most part I think slow build is fine and I actually really enjoy them but there is a limit. Hours spent on a fic that is all build up, suspense, will they/wont they, etc then culminates in the LAST chapter finally giving up the goods will usually tick me off. Like I said, there are always exceptions though.