Hello,
I will try to answer some of your questions:
Proxies: You gonna use them to avoid getting chain banned on all of your bots if one gets banned. So I would suggest to bot probably 1-5 bots on the same proxy, depending on what exactly you are botting.
VPN: Is also used to hide your orignial IP. You can use it for safety between your home ip and the proxy or use it straight to bot ( I wouldnt recommend that, cause vpn ips are often blacklisted)
For 20 Bots you probably need 1-2 VPS Servers that your bots can run 24/7. The other questions like which levels you should do manually and tips like that no one will give you. Try it out for yourself and improve it next time when you get banned.