That's Dtech's opinion - It's simpler to have a dedicated machine for the fact that you can control every aspect of the server and one of those being kernels and additional OS tweaks (advanced)
This is a good idea and as long as you are managing the master node to control additional security updates downstream.. I see nothing wrong with this. KVM is going to be far more superior to OpenVZ. You can test out installing QuickBox on a KVM node by spinning up a quick Digital Ocean droplet.
QuickBox will handle multiple drives as long as they are in a RAID array. 8xHDD in RAID10 would be good, however; make sure this is a Hardware RAID and not a Software RAID. Since this isn't data critical info, I always tend to lean towards RAID0 for speed and total combined space usage. The only downside to this... 8 HDD increases your chances for one drive to screw the pooch if it goes upside down. I would certainly run some SMART tests after receiving these, if they're relatively new, RAID0. Older drives I would examine more redundancy in the off chance there is a drive failure.
QuickBox does not choose for you as it is looking for either a /home or /(root) partition... not RAID, this is up to you.
Anything over 2GB is typically OK, however; if you are running a beastly setup and want to run multiple applications and scripts/custom scripts. I would at least get 8GB. SWAP isn't critical, but I would shoot for at the very least 2GB. This is not for the sake of QuickBox.. it's for the additional applications running that you choose to install on your system.
You may not be able to seek out OS & HDD tweaks etc that can utilize the server and it's network to the fullest, but you should still be able to seed just as good as anyone else. All that matters is Network and Hardware, i.e: Disk throughput. If you opt for a provider with a crappy network, then you'll get nowhere. Online.net, OneProvider (Online.net reseller) and Hetzner are splendid options.