1) where can I find character's AI controls? I have looked everywhere.

2) how do I move less than all of a given consumable? I can move all of them or none of them, but I have not figured out a way to move, say, three potions out of a total of five.

Both of these questions are answered within the game's included help system. I'll first tell you how to access it in case you have other questions later on.

For companion AI assistance, hit the 'J' key to bring up the journal tab, then select the '?' icon from the column on the left. Read the "Companions" tutorial. I believe this appears in-game early in the initial level.

For inventory management assistance, hit the 'I' key to bring up the inventory tab. In the upper right corner of that window, click the '?' icon for help.

Now for the direct answers:

1. Click a character's portrait to select him/her. Note the column of gold icons to the left of the selected character's portrait. Right-click the topmost of these icons to adjust AI settings.

2. Alt-click a stack of items to move only a portion of them.