Thank you all for the tips! Very useful stuff!
I'm new to Macro photography, so I think that for now I'll take the 100mm L and the Speedlite with the Rouge small softbox kit, and in the future if I get serious I'll take the 180mm (hopefully updated), the Macro flash and the focusing rails!
Thank you all again!
That's a good plan. If you outgrow that setup, don't forget there are cheaper alternatives to getting more "serious," e.g. using extension tubes with 100L to get more than 1:1 mag, using a good non-Canon ring flash (not continuous LED "ring flash").
I have used this one with good success. Still, I'm sure there are QC variations, so I would buy from a place with hassel-free return policy.