Is there any limit for how many active Steam Community Marketplace listings you can have at once? I have about one hundred Steam trading cards to get rid of.
Nope, however if you've not yet approached 200 sales then you'll need to either provide your name, address and Social Security Number or declare that you're not a US resident for tax purposes, depending on your situation. I sold dozens upon dozens of cards myself last year in the lead-up to the Autumn Sale, signed the aforementioned declaration form when asked, and continued selling through my stash moments later.