I posted this in the MK8 game promo thread, but I figured it was worth a repost here:
My Wii U has about 4GB free after installing all the MK8 reward games plus Game & Watch from the Club Nintendo rewards plus a few others like Wii Fit, Wii Sports Club, Toki Tori 2 (which is about 1GB), a few other Wii U shop games, not to mention several VC titles.
I did have to delete all the demos but I wasn't using those anyway. I also deleted the Rayman Challenge app but I could put that back on if I want. I'm guessing I don't have quite enough room for Smash Bros. which is a game I'd definitely consider getting digitally since we will go back to it so often. But with the lack of space, I'm leaning against that. Nintendo really should have pushed for at least 64GB in there. I mean, I guess 32GB was cool until they started offering all these digital promo games. But now that is getting overwhelmed!
I know people could look up the numbers and add it all up but you never know how much the system plus other utilities take up and how it all fits together until you actually do it.
I also know I could get a powered USB drive, but that is just sort of impractical where I have the Wii U placed so I will hold off on that for as long as possible. If the only reason I need it is for Smash Bros, then I have to factor that into the cost of the game. I could always delete something like Wii U Party, but I was hoping having it actually on the drive would lead to someone playing it

.
TLDR version: A Deluxe Wii U has enough capacity for all the MK8 promo games plus Game & Watch with several GG left over...