So for this, we just pick the type of mech we want and then allocate the money you give us at the start to customize it?
Have you decided how to handle money? I would suggest setting a minimum price for every mod you want included. People could then pay over the minimum price to gain improved versions (Perhaps every multiple of the minimum price is a level for that particular mod).
Romans 8:31 What, then, shall we say in response to this? If God is for us, who can be against us?
1 Corinthians 13:1-3 If I speak in the tongues of men or of angels, but do not have love, I am only a resounding gong or a clanging cymbal. If I have the gift of prophecy and can fathom all mysteries and all knowledge, and if I have a faith that can move mountains, but do not have love, I am nothing. If I give all I possess to the poor and give over my body to hardship that I may boast, but do not have love, I gain nothing.