1. Yes, pull of original cap (not hard at all its not glued on or anything) then put DaveC's cap on the stick.
2. Energizer 2500's work for me with a 15 min. charge time.
3.depends what you plan to do. I use 1.21 because somethings wrong with the sound quality in 1.4.0.
4.Depends on where you live but either Lik-Sang, Gp32z, or Gbax.com. And of course theres always Ebay