I started with 1k on amazon payments once a month in a lump sum.
Then graduated to 6k using serve and paying no fees.
I then got my wife a serve card and run 6k through her serve card. But using credit cards she is an authorized user for. I'm the main account holder.

This totals 13k a month in (no fee) MS split up on two cards before my regular spending. With my regular spending I will end up running about twice my yearly income through credit cards. I haven't been doing it long (3 months) but so far no problems.