You can use FF’s or Chrome’s cookie files: http://aria2.github.io/manual/en/html/aria2c.html#load-cookies

I would recommend Aria2. It can download several chunks of a file in parallel, resume downloads automatically with a set number of retries, it supports mirrors (maybe not an option for Google Takeout, but for other cases), and it can dpwnload over many different protocols.

Yeah. It’s a good idea to guard against it, but I would still never put spaces in filesnames that I myself choose.

Spaces in file names will always be fiddly though. It’ll work, but it’ll still be wrong, because arguments are space separated, and having spaced file names totally messes with that.