Itch has a key based API that this uses, and Playdate has no API, so it needs to use username/password to log in. I currently have it set to use a json config file which you put in your ~/.llpdmgr directory, which can be set read only. Once an api is available for Sideload, I'll use that.. but for now this is all we have. :(
Yes, it should, It's Electron/Nodejs so if you can run other Electron apps (eg Discord), you'll be fine.
And yes, it will only upload new/changed files. I will eventually add options to only show updated items, or auto-update, etc...