How many cards can I access in R&D / HQ?
It's in the official rulebook, under Access Phase in the section on Runs:


  • R&amp;D: The Runner accesses the top card of R&amp;D, and any upgrades
  in its root...
  
  • HQ: The Runner accesses one random card from HQ and any upgrades
  in its root...
  
  • Archives: The Runner accesses all cards in Archives and any
  upgrades in its root...
  
  • Remote Server:  The Runner accesses all cards in the server.