1. Their steel panels are not nice IMO, definitely prefer 3mm aluminium.
2. FPE could do them. Modushop should advise dimensions. I’ve done this with several of my builds (Modushop heatsinks and brackets and Cam Expert have milled the panels.)
3. Cam Expert accept FPE files, that’s what I’ve been suppling them with for years.
4. No experience with CAD software on a mac sorry, what I do initially is draw up files in Adobe Illustrator CC, then manually export x and y coordinates into Front Design, works well and is a great double check.
Soren has had some nice machining done by Modushop, I’ve used them for some heatsink drilling/tapping which was very nice as well, they were always good to deal with.