Well, i'm always a fan of even number raid groups. Even though netapp says you can go to 28 disks in a sas rg, that risk profile is too high for me.. 23 is pushing it a little as well.. Highest i've gone was 24, in isolated cases.
I suggest you read the following document - reallocate best practices tr-3929
I still don't understand why netapp never thought to re-allocate the entire aggregate when adding disk. That would be a big win. It's a tedious process, but if you want to stripe the data across all your disks, this is what you will have to do