SQL Server configuration / specification recommendations and advice!
What I'd do


4 disks for RAID 10 for all log files
Disk RAID 5 for all data files + OS
Don't bother with RAM disks


Why?:


With 24GB RAM all databases will be in memory so RAID 5 doesn't matter because disk reads won't really happen
Write performance is determined by log file throughput
Data files are larger then log files so RAID 5 is more efficient


What isn't ideal:


Not having one volume per database log file
Separation of local backup drives
Not having separate RAID 1 for OS + binaries


Other options:


Define "heavy write": you could go to RAID 1 for LDFs and another for OS for less than a few million rows per day