It sounds like you're limited by computing power/resources in terms of creating a sustainable bot farm. Nonetheless, here's some tips!
A few things you'll wanna know:
OSbot SDN = the official script repository for OSbot. Every free/paid official script can be found here. If you're logged into OSbot website, you can add scripts and they will automatically appear in your OSbot client [as soon as you refresh the script list within the client].
Mirror mode = mirrors actions on the official OSRS client, which means you'll need both OSbot and the old school runescape client open. Therefore, it's more CPU intensive than stealth injection, but generally considered safer.
Stealth mode = injects code into the game client itself. Runs within OSbot client, less CPU intensive. Riskier than mirror mode.
I'd avoid VPN in general, but maybe others will disagree. You can use proxies, VPS, or VMs. Info about all of those can be found on these forums. Many scripters and community members can help there as well.
General tips:
F2P is riskier than P2P for a number of reasons.
Botting tutorial island may increase ban rates.
Take breaks.
Think like a human player... would they grind unicorn horns for 13 hrs straight? Probably not, so you shouldn't either.
Put some clothes on your bots.
don't be afraid to experiment!
**edit: you can use "cpu saver" or whatever its called, it can be found in the osbot client settings somewhere. Might help with the resource constraint.
Best of luck out there friend.
-Dan