AAdvantage will change their mileage earning to spend-based later this year (miles will be awarded as status-based multiplier of fare paid, regardless of distance flown). It is currently unclear how partner earning will be handled, but expect a major devaluation from the current status quo. I would definitely wait for this to be officially announced in a few months.

As award seats come out of the same inventory bucket and are made avilable to all alliance partners, it shouldn't be a problem to redeem MP miles and/or AA miles for available seats. I have done cross-program redemptions with multi-passenger awards before, redeeming AB miles and AA miles for seats on QR flights...

You should be able to access the CX lounges with your CX status regardless of the FF number that's attached to the itinerary. Just show your card in addition to the boarding pass. That's one of the very few occasions one needs the physical card nowadays...

One thing you need to be aware of: AAdvantage is now enforcing their long-standing minimum segments rule. You must fly at least four segments on AA-marketed and -operated flights in order to qualify for AAdvantage status. If you only fly Alaska and CX, you will not be able to gain AA status.