We've split between CSS and CSA and did 11 nights (5 at SS, 6 at CSA). The transition isn't bad - it takes about 3 hours to go from one resort to the other. We started at CSS and ended at CSA. We were very much ready to move to CSA as we weren't having good weather at CSS and that resort really wasn't a great fit for us.
I think I would be fine with 11 nights at just CSA - but also, previously, we stayed at CN 12 nights and found that to be too long. We've found that 9 or 10 nights is the magic number for us.
Since you want to be active, I think switching resorts might be a good fit for you, and I don't think you'd feel rushed at either place. If by active you're also including fitness (working out, etc) CSA's athletic center is AMAZING.
Melea & Joseph
CN - '06, '07, '08
CSS and CSA - '09
CSA - '10