I do not use loadlin as I have moved away from Windoze. I use "lilo" and find it quite gratifying. I will respond as if using that mode:
1) If using lilo each hard drive(hd) is effectively a logical device. Simply partition the drives for your Linux features required (i.e. /, /boot, /root, /home, /opt, /var, /tmp, etc. plus of course swap (3x memory). Note which partition you will boot from. Lilo is quite capable of allowing you to move stuff about but the system must be re-installed to match physical and logical partitions.
2) I will defer on this one as I use the master boot block in the "WINDOZ" partition but I do know you can do it in a Linux partition (see "Running Linux" or "Linux Essential" I think both cover this).
3) Why limit yourself. I have between 9-12 different window managers I can use from a script I call "wm". Basically this script points to each window mgr startup script and dumps it to initrc then does a startx. Thus you boot to a text window do: ./wm select the mgr desired and stand back. An yes you can setup things to allow you ot boot directly to the win mgr of choice.
4) /var does NOT need to be a primary. My recollection is that SWAP does but that does not seem correct as one can have multiple partitions for swap. Check one of those sources I mentioned.
PS-- The only good Sys Admins on *nix keep lugubrious notes then wished they had made more.