For "real" scratch drives (temp/swap), I would go RAID 0 or use some of your 24GB memory in a ramdrive
For boot drive, I would use a small 100MB partition on your HDD
For OS/Apps drive that the boot links to, I will create a SSD partition on a RAID 5 array taking care of having the RAID 5 stripe size to equals the OS "page" size (Windows cluster size can be up to 64KB)
For scratch Data drives, I will use the OS/Apps partition above
1. No known problem if you know what aligning a partition is and if you have no useless background process (defrag, index, etc)
2. The TRIM function can not happen in RAID...and, in most case, you don't care at all because it only helps the garbage collector (GC) to know at deletion time whose sectors are to be resetted later on. In many situation, you only update sectors which means the SSD write on new sectors and marked to-be-resetted old ones. Obviously, if you leave enough free space (you already have 10% invisible "spare area" in all SSD) which is your case
3. SandForce 2000 series based SSD are the best as of today, Intel's are almost equivalent but don't worth the price gap to my opinion. Most SSD manufacturers provides TRIM alternatives (Intel's Toolbox for example) that "refresh" their SSD.