Paper most important
You are correct, Argyrotype is most particular about paper. I have been using DIY sensitizer since Feb this year and have had bother finding useful paper. I love Kallitype on COT320 developed with sodium acetate but was hoping for a longer tonal range. Argyrotype doesn't work on COT320 or Platinotype. I suggest you start with Whatman CP paper (from New York Central), lovely rich brown dark tones and cheap too. I have tried the new Weston diploma parchment but can't recommend it because the image doesn't stick to the paper during washing. I am now using Buxton but it is not exactly working and so expensive that testing is out of the question.
Good luck and keep us posted as to your Argyrotype adventures ... John