• I think on this system it'll be better to run Ubuntu directly, so there isn't a need to run VMs for the different services (at most Docker)
• Back blaze might not be too bad if I wanted a backup-only service, and I would then have to stick with Nextcloud. Kinda wanted to stick with GDrive for GPhotos, but Syncthing could be a good replacement for it.
• I have a VPS with them right now, and the lower tier plans will sometimes let you go above 100 Mbit, but the sustained guaranteed speed is 100 Mbit. The higher tier plans are gigabit guaranteed though.
• Answered by first bullet point, would rather not bring the Xeon system home since it's huge and might suck up even more power, let alone using the two at once.

Thanks for attempting to answer all 4 questions though, the most important question I still have is which filesystem to use, one that can be expanded from a single drive to RAID 1 or 5/6.