Mathias,
Normally, it's highly recommended that you have a single aggregate dedicated to the root volume. In some cases, where you never plan on having more than a shelf or two, that's a big waste. If you don't plan on adding a lot more disk to your controllers, it makes more sense to expand aggr0 and have only one aggregate per controller. If you will be adding more disks over time, leave aggr0 alone and create a second one with your remaining disks. Make sure and leave at least one hot spare disk per shelf.
Per the Storage Management Guide: https://library.netapp.com/ecm/ecm_download_file/ECMP1141781
You should size your Raid Groups between 12 and 28 (recommended between 12 and 20), with all RGs being as close to the same size as possible. With what you have, assuming I would not be expanding again anytime soon or with very many disks, I would do the following:
1 shelf per controller.
1 aggregate per shelf, size 23 disks (1 hot spare).
Raid Group size 12 (1 RG size 12, 1 RG size 11).
Decide what best fits your needs but these guidelines should help (I hope)
