Well, let me start by saying that with the default Boot Camp tools, you probably won't be able to setup more than the 2 OS partitions on the internal drive of your notebook. Not that it can't be done with other tools, but it is not a quick and easy setup to do, so if you are going to undertake it, please be prepared for issues, and do it from the beginning. There is a decent thread on this forum about "repairing after you change your partitions" which has plenty of information about the problems you will be facing and how to work around most of them.
Having said that, when I was using Boot Camp on my MBP with a 750GB drive, I gave 500GB to MacOS, and 250GB to Windows 7. I also used Paragon's NTFS for MacOS driver, and Paragon's HFS+ for Windows driver (after having use MacDrive for several years). This combination allowed both OSes full access to the entire 750GB drive, and I put my Thunderbird and FireFox profiles on the MacOS partition, but could access them from either OS that was booted. That solution worked great for me for years (until I upgraded my MBP and opted to eliminate Boot Camp and only run VMs for Windows).
With the proper drivers, either OS would be able to utilize your external drives, but keep in mind there are still some Mac utilities/apps which will only work with an HFS+ formatted partition, just like there are some Windows programs that do the same with NTFS. Personally I found that I would have to "share" my external drives with other Windows users more than Mac users, so I formatted most of mine NTFS, and just took the minor performance hit when accessing them under MacOS.
