After a visit to my local India Bazaar and not finding any henna that interested me (sucks too, because it's a big new one right down the street from my house), I've done a little research and decided to postpone my cut and color until next weekend. *sigh*
The good news is my research also yielded a lot of answers regarding my technique. I decided to nix the amla and use it with brahmi every other month, alternating with henna. (Assuming all goes according to plan.)
I will definitely shampoo and condition first and apply the henna to freshly washed, slightly damp hair. I'll cowash the henna out and follow up with a good thermal DC.
I won't add an egg--yet. Just chamomile tea and lemon juice (2:1) and enough honey to make the paste smooth after the dye releases. I anticipate this will also add a conditioning effect that will enhance rather than impede dye uptake as adding traditional conditioners or oils likely will. Besides, I'm not terribly worried, since I'm sandwiching it between conditionings. We'll see if this needs to be amended later. I guess I'll find a henna thread to pose my remaining questions, lol.
Be back next weekend with pics...