Yes TRIM does not work with RAID, so the best you can do is to use the whole disk (do not create a smaller partition and leave unallocated space) and try to have at least 10 GB free. Unfortunately, you will have after a while to unRAID the disks and clean them seperately to restore them to their initial performance state.
Unfortunately, I cannot help you with the RST drivers since I haven't used them.
do I need to (or should I) install the Intel RST Drivers?
You don't need to install the Intel RST drivers, but I do recommend it, because they are optimized for being used with Intel SSD's running Win7 (32/64bit).
The currently best RST driver for me and my Intel RAID system (ICH10R with 2x160 GB Intel Postville SSD's as RAI0) is v18.104.22.1681.