Beware you don’t really “compress” the videos like zip files but rather re-encode them, which is not lossless. Encoding is a very computation-heavy task that can only be brute forced with more raw hardware power.

You should make more research and experiments before doing this, no one can give you a “one size fit them all” solution when it comes to encoding.(i.e. you want to prefer speed or quality, there are tons of option) For starters if your GPU supports hardware decoder+encoder you can use it to speed up the encoding process, this is far faster than using only CPU to decode and encode.

Have a look at what HEVC is if you want to have good balance between size while preserving quality.

HandBrake, doesn’t compress them, it reencodes them, slightly different. Anyway, for your purpose, H265 software on CPU should get the best results. try with a shorter video, with different settings to have an idea of the end result (you are gonna lose quality in one way or another, how much and where depends on you). Then simply let it go overnight, depending on how many files you have, your hardware and your settings, it can easily be 10s of hours. Get an idea of how much time it takes and do it in batches if you are gonna need to use the pc during the day for example. You could limit the program to only use a certain amount of cores so you have some left for you daily use, but if you game for example, its a no go. encode during the night, play during the day

it would be faster to download them in a lower quality rip. or just buy a bigger drive, storage is cheap, your time is invaluable