Well, there are three questions you need to decide on first!

Question #1 - Is the mech combat the main focus, or does much happen out of mechs?

If the former, character sheets should be heavily stripped down, and mech abilities that characters have should be purchased in a seperate pool from non-mech abilities. If the latter, you can have more developed characters, and they can buy their abilities from the same pool. Generally, I would recommend seperate pools (so no Abilities or Skills affect mech piloting, but you get a set of Mech Feats or something that can only affect mech piloting) regardless of how complex you want the players.

Question #2 - Are Mechs Equipment, or Characters.

If mechs are equipment, then individual parts probably have a cost, and players are often going to be climbing into other mechs, and damage or destruction is going to be fairly common. In addition, mechs will be heavily customizable, most likely, since you can just kind of buy parts. You'll want to have rules for upkeep and maintenance, and players will have to worry about splitting money between their mechs and their lives.

If mechs are characters, you're going to be balancing them not just with cash, but narratively. XP can go towards Traits that modify the mech without being literally bought, and you can handwave money as "players get Mech XP instead of money" and not worry about actual cash or upkeep costs.

Question #3 - What resolution mechanic are you thinking of basing the game on? D20? Storyteller? Cortex-derived? Percentile? Something totally weird, like drawing cards out of a deck?