Era isn't terribly relevant - if you stick with the fancy dry erase colour cards that come in the forcepacks with the mechs you should be ok (there aren't too many that are too nuts for strange tech). I find giving each player 2 mechs - a medium and heavy, or light and assault - roughly equivalent PV, all starting skill 4, is a good way to ease players into it.
Alternate Ammo is something I'd reserve for after someone has played their first game.
Giving the players an incentive to fight over is helpful - like an objective in the center of the table - helps get them moving towards each other.
