By default you can only queue up 8 things. The "range" in the XML for this is "1-10". So I changed it to 10.
But I also changed it to 15. 15 seems to work fine, but since the XML specifies 1-10, I am considering it "in testing". It's just a mod so removing it will fix it, anyway. 15 takes up the entire length of the top of the screen (at 1024x768 resolution, at least. I think the default of 8 is so that low resolutions can see the whole queue).
Issues: If you use an interaction that is wider than one tile, interactions will queue off screen. So if you have a sim sitting on the bed and reading, showing the chair and the bed, that takes up 2 "slots" and the 15th interaction will be off screen. Or if your interaction sequence includes going somewhere, that also takes up extra space.
Only use one!