To add to my post was just trying out the zerg brutal key farm. It farms the keys no doubt! BUT it gets stuck a lot! From an attacking mob just one mob. I will not kill anything just stand there while my companion trys to kill it. If there is a group of mobs blocking my way I will die cause it will not attack them.
Most of your other queries have been answered, so I will answer your Zerg question. Currently there is an issue with zerg mode with certain objects in the game like corrupt growths in Act 4. The bot will simply stand and stare at them.
This logic applies to other issues with being stuck on objects or enemies. You could also wear boots that allow you to walk through enemies.
DyingHymn's response to this in his A4 Bounties was to use a character with pets for these types of profiles. This way your pets will break down the enemies/growths based on their in-game AI.
In short, most of us are just avoiding the zerg profiles as the normal options seem to target these objects with much greater consistency at this point. To answer your followup question to this, xvjz has been re-working trinity and has posted such in the Trinity section of the plugin forum [2.1 BETA thread].
As far as the max sessions, this is because while you bot may have closed, your demonbuddy session might not have. There is a timed delay before you can open up another session I believe... I just reboot my PC when it happens and whether it's the reboot or the 30 seconds until my desktop comes back up, I am always able to log back in.
In closing, checkout some of the first time user threads for some more basic information on how to properly setup and use DB.
There are some very useful tools that I didnt start using until 8 months in. rrix's YAR plugin is an amazing one. YAR stands for Yet Another ReLogger. In short, if your game crashes, it will start a new instance of DB and restart your bot. You can also set time blocks that the bot will turn on and off to make your account look more legit.