You can place four drives in RAID-1, but it is up to the software if it can accept four queues. You can try set up multiple RAID-1 arrays and then add them to either LVM2 or EVMS, but the system will not be able to access more than one file. You can setup two LVM2 or EVMS and put them in a RAID-1 array. Two files can be read at once and the capacity can grow when needed. With any LVM2 or EVMS setups, it will try to do RAID-0 when possible. If the server is going to have a 50/50 read and write queues, two RAID-5 hardware arrays and Linux software RAID set in RAID-1. This will provide multiple write and read queues. Also it has higher reduntancy rating than RAID-5.
I never seen a site that is taking up more than 72 GB. If you are setting up a file download site, than maybe. I think this site is taking up a few gigabytes.