This depends on what version you are playing. If you know what type each of the Elite Four uses, you may be able to teach moves accordingly through T/HMs or by level to give you an advantage over your opponent.
You should train your Pokemon over level 50 and teach it good moves. The elite four are actually quite easy but Lance is your toughest guy to beat.
No you need a Pokemon GBA game like emerald and on the title options click migrate
Of course this depends on your pokemon. My team's best moves are fire blast, flamethrower, surf, hydro cannon, dragon claw, dragon breath, fly, and earthquake.
anything :P
you train it to level 95 or up and teach it good moves or action replay cheats
If you have the TM Night Shade, you should teach it to Misdreavus. Really, it is a judgment call depending on your Misdreavus' moves before evolving.
Teach salamance Dragon Dance,Outrage,Earthquake,Stone Edge.
Charge, Discharge, Endure, And Endeavor
You should teach HM moves to a pokemon that you will not be using, as you can't forget HM moves until you get to a move deleter. Grass type Pokemon's can usually be thought cut.
no because it already has good moves
chipaway rockthrow rocksmash and low kick
you should teach it earthquake, Thunderpunch, Ice Punch and cross chop to get ice punch and cross chop, breed electebuzz with a medicham and that egg will level up knowing those moves