1. No you can't fdisk while installing. You can add drives afterwards, however, and mount them as you please. I believe there's a howto on this somewhere.
2. Just make sure you use Red Hat 7.1 packages. I find the easiest way to get these is using rpmfind.org
3. I'm sure it's possible, exactly how to set it up I couldn't say - haven't used dialup much.
4 & 5. Again, it's possible, but I don't know if it's been done, or how to do it.