1) Experiment. See how much you need to dissolve 1g at the temperature you want to use, then just multiply.
2) Yes, or preferably by vacuum distillation of the freebase, but I assume that is beyond your capabilities.
3) Huh?
4) Yes, it is very much reccommended that you gas the freebase with anhydrous HCl, followed by recrystallization of the HCl salt from ethanol, methanol or isopropanol so that it becomes pure and sperkling white.