I was completely with you until #5! I'm assuming you mean something that will pick up the cutting information from the auto-ganged/imposed job. Can't help you on that.
As for the rest of your points, there are many RIPs out there that will do that for you without extra ganging/imposition software. Points #1 and #2, virtually any RIP that has a ganging/nesting feature will do that. Point #3, some RIPs will auto-rotate for best media usage, others will not rotate when they nest. Point #4, again, some RIPs will gang/nest based on roll width only (good), others will base it on a "sheet" even if you're using rolls (not so good). The better RIPs will allow you to define the nesting/ganging using either method. GMG Colorproof and EFI Colorproof XF are RIPs that meet your needs for points 1-4 and there are other RIPs I'm sure that will do that as well.
As far as software, I'd take a look at ImageNest by BlueCubit (Software RIP : ImageNest for Mac OSX). Very slick software. Combine this with a ColorBurst RIP and you've got a pretty cost effective solution. You can also use ImageNest as a "RIP" as long as you don't mind using RGB profiles via the printer driver and forgoing a lot of the more advanced features in CMYK RIPs such as ink limiting and linearization.
Regards,
Terry
Terence Wyse, WyseConsul
Color Management Consulting, G7 Certified Expert