Yes, but you also have to consider that by the time you come to add more it is probably going to be just as cheap to buy a bigger drive(s) and replace the smaller ones, sell of the old ones. I'm not saying do get lots of slots, but think over all of the options, like you said an adapter card.
I might go down the zen 3 route if performance v price works out, but would certainly want a board with 3 x M.2 slots and not have to bother with an adapter card.