Assuming 7-mode...
I would have one big aggregate on each controller, which means I would expand aggr0 to become 4 raidgroups of rg size 23, raid-dp. Reasons:
1. Hate wasting 3 drives for just vol0, especially if the drives, which you didn't mention, are large-capacity (e.g. 900GB SAS).
2. We use rg size 23 because we tend to add storage by shelves, and it's a lot simpler to grow the aggregates by entire shelves. Plus the disk drives keep getting bigger and bigger, so it's just really easier to deal with entire shelves at a time.
3. We like larger aggregates, and less number of aggregates. Lots of spindles for performance. We like to have one SAS aggregate and one SATA aggregate. You don't have to deal with aggregates running out of space and you have to migrate a volume to another aggregate, etc etc.
4. Less wasted disks drives.
We had NetApp consultants here for three months and this was one of their recommendations. It took me a lot of work merging aggregates (one filer pair went from about 20 aggregates or so, down to 4) and we're really happy we did this.