With SAS drives you can put up to 28 disks in a raid group or as little as 3.
So just create a new aggregate and put 23 disks in the aggregate and leave one as a spare.
The raid groups will automatically be created for you, however you can adjust the amount of disks before a new raid group is created in the aggregate.
I'm less conservative when it comes to this and take full advantage of 64bit aggregates, so I agree with what you're trying to do.
Here are some Pros and Cons,
Pros: Better capacity, ability to create bigger volumes in return for bigger dedupe savings, and more iops.
Cons: More exposure to a double disk failure and longer rebuilds on a disk failure.
You could go a little deeper than that, but for me, these are the biggest factors. If you haven't already, grab OnCommand System Manager 2.0.2 from the downloads section on support.netapp,com and do it up!