Here is my quick maths on the probability of success/failure assuming an attribute of 11 and a roll greater than DL. The "Prob" column contains the probability of rolling at least that value. So you can see a 50% chance of success/failure with a stat of 11 comes in at DL 21. So I will probably end up using a range of 17, 19, 21, 23, 25+ as that sets the middle at 50% and the upper/lower bounds at about 10%
Regarding fan content: Thank you! I'll start working on some stuff and run it past you when it's in a good place.
Edit: more math! I wrote a little python script to brute force the expected number of uses you can get out of UD. These numbers are in average after 10k iterations.
6: infinity
5: 14
4: 8
3: 5
2: 3
1: 1
0: 0