However I'm having a weird time with pronunciation of ll in Andean words. I have an instinct for it and I think I get it right when I'm not thinking. But if I consider for more than one second, I'm lost in indecision: is it an l-ish sound or a y-ish sound his time? Is there a rule I don't know?

I’m so glad you’re enjoying it. Can’t wait to talk more about it. My understanding is that in Quechua before a vowel LL is y, and before a consonant LL is L. Yllapa v mallki, or Yyyapa v malki.