I don't think there is a size limit to decks, I have a deck that is 375 cards big. I will howerever take the moment to chime in that the mass uploader for deck images breaks and if you do too many mass uploads back to back the previous uploads tail end images will upload into the next mass upload. I reported the bug but they never fixed it. So if you are uploading lots of deck images, after each one, get up, stretch your legs, walk down check the mail, maybe feed the pets, then come back and upload another batch!