Do you need to modify the install media in order to use expect? I'd like to read more about the process.
You can netboot Linux. Knoppix [1] offers Terminal Server which configures DHCP, TFTP and NFS so that you can boot Knoppix from the local network.
Yes you do but you usually netboot to do large installations so this is just a case of adding a new root device with some extra tools on it on your netboot server.
There is an official solution in -current that involves DHCP but I don't know the details.
Yes. You can use expect with /install easily and you can simply add your own local "site set" tgz which can be hosted on a local HTTP/FTP server to apply any local customisations.
However, if you're provisioning lots of machines, it's very easy just to "restore" filesystems off a bootable USB stick, mount them, set the hostname then tell ansible/puppet to do the rest. Don't need kickstart or any of that crap.
Personally though I'd just netboot lots of systems off PXE/TFTP, NFS mount all filesystems and have local swap disk only. I used to do that with Sun systems. We had 50 SPARCstation 5's booting off a SPARCserver 1000E on Solaris and it worked nicely. OpenBSD works pretty much the same. Linux is a piece of crap to netboot.
Plenty of ways to skin that cat.