I'm not too sure about Heliamphoras as I have never grown them, however I would suggest a 1:1:1 Peat:Perlite:Sand mixture for the Cephalotus. Here is a great website that also has information on Heliamphora substrates:

http://www.sarracenia.com/faq.html

Well, you just stepped up your CPing a few levels. No, Heliamphora will get very angry with you if you try low humidity levels. It will get very angry with you if you don't give it lots of light. And it will get really really angry with you if you let the temps consistently get above 85 degrees.

Dave Sackett of the NECPS recently gave a talk on growing Helis. He uses Cypress bark mulch topped with live LFS as a potting medium. His Helis really look amazing and he has won awards for them at the NECPS shows.

I grow my Helis in tanks in the basement - nice and cool.