Hi,
CReating single disk group is not going to help you use the virtual feature of the MSA which is automated Tiering.
Automated tiering
A standout capability of virtual storage is automated sub-LUN tiering, which can increase overall system performance at a lower cost than
possible with only one class of disk drive. Automated tiering distributes the contents of a volume over multiple virtual disk groups within a
tier as well as over multiple drive classes that are grouped to form a pool. This process exploits the performance benefits of a particular drive
type, but only for the part of a volume that requires
For more info please read page 11 https://psnow.ext.hpe.com/doc/a00087404enw
Yes you can have RAID 10 and RAID 5 in a same pool.'If you want to enchance performance you can add SSD drives to use as Read cache/Performance tiering.
It completely depends on you of how many disk groups/tye of drives you need to create based on what is your requirement.
Please also read best practice guide I shared that might help.
Thanks