I've been playing around with something similar with a desktop. One suggestion if you've got old/spare/small drives is bcachefs to handle combining SSD and HDD,

I've been playing around with something similar with a desktop. One suggestion if you've got old/spare/small drives is bcachefs to handle combining SSD and HDD, multiple of each even and with different sizes. I haven't been running it long enough to comment on stability (nothings gone wrong yet), but it's nice to not have to manually deal with moving files around, especially during the initial transfer of games. It's just for games, I'm not worried about losing files. My old laptop has an mSATA 64GB SSD. None of my other devices have an mSATA slot, I don't even think it's worth getting an adapter to use it anywhere else.