What kind of Solaris 8 install is the first question. I would start with an end-user install. But I would use the custom mode and add some stuff. I find that it is easier to add stuff from end-user than it is to go with full+oem and remove stuff. But putting Solaris 8 on a 4 GB disk is a tight fit and some choices will need to be made.

The first question (sizewise) that the install will ask is swap size. I would go with 1/2 a GB with your disks. A second swap partition can be added to another disk later.

A damaged root can mean that you can't boot the system. I think root should be small with no user-writable directories. I also think that you should be able to boot the OS with only the root disk. So I keep the core OS on one disk.

After you make your choices as to what gets loaded the OS will ask you for partition sizes. At this point, it will know how much it needs.

I would use a separate /usr. The install will give you a min size. Multiply that by some factor between 1.5 and 2.0 and use that. You may want to have a /usr/local later on. You can put that on another disk.

/var should be large. I would go will 1 GB even with a 4 GB disk. /var/adm, /var/log, /var/spool,
/var/crash, /var/mail,.... the list goes on. /var can consume disk space fast. Make it big.

/opt may be so small that you can leave it in root for now and maybe move it to another disk later.

You can use disksuite to mirror the root disk if you have an identical disk available for the mirror. But that will require a tiny slice for the disksuite database. If there is any chance that you want to mirror, make the smallest possible filesystem and call it /disksuite. This will leave the mirroring option easily open. Never put anything in here.

After you have made choices for /var, /usr, and maybe /opt, you can adjust the root size. Because it knows how much was moved out, the install program now knows how much it needs for root. This should be rather small. Double or triple the min size and go with that.

Call the rest /export or something.

This should give you an idea of where to start.

Immediately after the install, install the cluster patch. I see no problem using -nosave for this patch (only). I see the install and first cluster patch as a unit. But with a GB in /var you will have the option.