Thanks! Very tempted. Really shouldn't get myself any more toys to tinker with, but it does sound like fun...1. Not so you'd notice- 64Gb is eMMC, 256+ are NVMe. Very little practical difference.
2. Absolutely yes.
3. I've used a wired (Xbox) and Bluetooth (8bitDo) controllers with no issues. If Linux supports it, it should work.
4. No idea, happy with SteamOS, but some here are having a decent experience with Windows.
5. Looks like some here dual boot, might need a bit of faffery to keep working after updates. That's half the fun though!