New Zealand (South Island)
Seth Kenlon is a UNIX geek, free culture advocate, independent multimedia artist, and D&D nerd. He has worked in the film and computing industry, often at the same time. He is one of the maintainers of the Slackware-based multimedia production project Slackermedia.
Authored Comments
This probably isn't the right place for an in-depth discussion, but aside from IRC, I'm not sure what is. Instead of SVG or AI, try providing your clients EPS. I have found those to be very good intermediate files. That said, most recent versions of even Illustrator can open SVG files.
Separate+ is for "physical" (in the digital sense) separation of colours. If all you want is for an image file to be flagged as CMYK, then all you need is a quick conversion with Image Magick.
I don't see any reason not to use GIMP or Inkscape for such renderings (or both). It just depends on what kind of graphic app you feel you have the most strength in. I can imagine finishing in GIMP, just because you'll probably need various compositing modes to make the branding that you're applying look reaslitic, but some elements in some of those examples are certainly either airbrushed or just created by hand. Not really that complex, certainly not specialised. Give it a go!