Agree read the concepts guide.
3PAR is reservationless so there's no concept of having to create upfront constructs such as aggregates, pools or raid groups, space is really just a set of chunklets that are assembled and torn down on demand based on the policies (CPG's) you associate with a volume. As such the system will just assemble space on demand and this can be tricky if you're looking for absolutes, since depending on the CPG config, space can be allocated on demand in different ways to different volumes, so best try not to compare with EMC, Netapp or traditional raid systems
At a basic level CPG's are just a logical construct (not physical), the best way to think of them is as a policy or template that outlines how volumes associated with a given CPG should consume space as it is demanded by incoming writes. The CPG itself doesn't consume space as such, it just provides an aggregate view of the space consumed by all volumes associated with that CPG, but it's handy way to manage and monitor the layout and space consumption across multiple volumes.
Different stripe sizes are used for multiple purpose. Performance is one, as the smaller the stripe the smaller the parity calculation overhead, but this is minor unless you're really pushing the limits. Efficiency is another since the larger the stripe the less parity overhead and so the greater the space efficiency. Availability since a larger stripe size also carries a mathematically higher likely hood of an overlap failure and the variable stripe sizes allow the system to automatically guarantee things like cage level availability and to re-tune the system to best fit the changing physical layout over time.
Regardless of the number of disks you can create as many CPG's as you like since they won't consume space it's just a policy that directs how a volume will grow. Once you then create and associate a volume with that CPG say 1TB @ 6+2 then the system will create a minimal amount of logical disk space behind each controller as a buffer for incoming writes. Each of these logical disks will follow the CPG policy e.g 900GB, Fast Class, Raid 6, 6+2 meaning each logical disk will be made up of multiple independent stripes of 6 data +2 parity all glued together to form a single volume. As the volumes space is consumed over time these logical disks will automatically grow to accommodate the new data.
When you have multiple volumes associated with the same CPG they will share this underlying space, and the volumes associated with given CPG can grow to consume all available space assuming you have over provisioned that space. Typically you will have different CPG's with the associated volumes growing in different ways at differing rates since they're all thin provisioned
Parity overheads for the different stripes will be as follows.
2+1 & 4+2 = 33.3%
3+1 & 6+2 = 25%
4+1 & 8+2 = 20%
5+1 & 10+2 = 16.7%
6+1 = 14.3%
7+1 & 14+2 = 12.5%
8+1 = 11.11%
