- I didn't realize there were more than chooser fields, so I'm no help with getting the third to display.
- For the tag expressions, I usually go with this format for damage types: thingid.dtAcid. That always works for me when everything else is working properly.
- I'm not familiar with the "forward" function. I usually use perform hero.pushtags[DamageRes.?] and that does the trick (depending on timing, of course).
- Make sure you're establishing what pool of things the tag expression is pulling from. On the editor, this is the "Restrict First List To..." box. For this, you want to pull from all things. If you were to select All Things from that drop-down, you'd see it assigns the tag "ChooseSrc1.Thing" to this feature. I would recommend trying to add that and "ChooseSrc2.Thing", etc.
- I don't know if it's part of your text editor or something that you're using to pull this up, but my code within the editor never uses "&". I always just have "&". Again, might just be a translation thing from the editor to your post, but I'm trying to find anything else I can.
EDIT: Thinking about the third box thing; if all else fails, you can always make a second copy of this feature that just features the third box and bootstrap it to the first copy. It's less elegant, but it works.