McP77

I think I'd go Fast Flex.

I prefer an 8mm cutting wheel for porcelain. Scribe quite hard, try the breaker gently, if you're getting a lot of resistance scribe it again and try breaking again.

I don't use white grout on floor as it's so difficult to keep white, even if you seal it. Leave the choice with the customer at the end of the day. If they really want white you could consider epoxy but a lot more time consuming.