I now have 20-something "projects" uploaded.  But most of my projects consist of old, WIP builds which I set to private - just so I can revisit them later on and see my progress (and kind of as a nostalgia trip). 

Now, I'm wondering if there is a limit on the amount of uploaded projects you can have on itch.io. And if there is a limit, do some of your projects get deleted or something to make space? Am I straining the itch.io servers by uploading all these pointless projects haha. This probably sounds like a stupid question but I'm just curious. 

There used to be a cap at some point. It was increased, then removed, then (partially) reinstated, I think? In any event, if you reach a cap you simply won't be able to add any more projects. If that happens, contact support and ask for the cap to be lifted. It was only a safety limit anyway.