Ever thought about using LVM ?
I would do the first install with the following lay-out.
100M for /
32M for /boot
200M for /tmp
500M for /usr
250M for /var
100M for /home
/opt is not necessary because no software is installed there at first. I use it for all soft that does not come from an RPM package.
Afterwards, create a number of big partitions on your HDD which will serve as LVM physical volumes.
To use LVM, I would advice you to first install it via the RPM delivered with linux and afterwards install the latest production version from the source (http://www.sistina.com
Big advantage of LVM is that you can extend your filesystems when you need to.
Don't put root and boot under LVM. This will cause a lot of problems if you ever have a problem; LVM filesystems are not available from the rescue system on the CD.
Also a good idea is to make two root partitions and two boot partitions. If something goes wrong with one of them, you still have the other to boot from.
Probabely a lot of docs to read, but once you know how it works, you'll probabely love it.