First make it work on one computer. Every 4-core will handle 2x diablo3 + 2xDB. Use AutoFollow plugin on both. Played account will be server, bot as the client. Server will load TrinityNoCombatNoLoot.xml profile from
https://www.thebuddyforum.com/threads/trinity-compatible-combat-profiles.132380/ and the client will load FollowerCombat.xml from AutoFollow profiles. Set client's combat routine and all the typical solo DB stuff and you should be able to freely control the server (I vaguely remember it looted for me even the profile name suggests otherwise) and the follower will follow, fight, loot, autodrop items in town (if set to) etc.. Can't remember how town runs worked, if you force them on server, client should do it automatically.