I've got already some experience creating operating systems for the x86 architecture (I was the lead dev for an Open Source OS called "NonameOS" a few years ago). I've written the kernel, all the drivers, the memory manager etc. so I think I could help you out here.
I would propose to use as many Open Source libraries/components/code as possible here (if it's acceptable for you from the licensing POV) as it would speed up the development and keep the costs low. Also, assembler isn't the best joice for the WHOLE project - ASM for the "boot/startup" phase and then C for the rest sounds much better.
Please ping me if you're interested.