1) Yes, the 20 way seats are a must. THe most comfortable seats ever created in a vehicle. Well.... minus vehicles I have not been in like Maybachs, Bentleys, and other ultra luxury vehicles

2) They do work work but they don't so much cool as they pull air through the perforated leather. I personally like them and my passengers often enjoy them in the summer. You "feel" them more when wearing light summer clothes but can still be felt through denim. I'd say sit in them yourself if you can and then decide whether you like them. Also not that you cannot get the Napa leather with this option. The active part is an air bladder that inflates and deflates under your butt. It's nice on long drives but not really a true massage seat. I usually use them in short spans of 10 - 15 minutes.

3) No. Skip this one. Your 10 year old will outgrow them fast. The 3rd row also shortens the cushion on the 2nd row. The seats stow where the spare tire usually would be stored so you lose the peace of mind that comes with an actual spare tire. Plus they weigh quite a bit and will add to the already heavy vehicle.

As for the Sirius, you might be able to install it yourself for cheaper than the stealer price. I believe Circle BMW can sell you everything for several hundred less than the factory installed price. A few screws plus mounting bracket, hook up a preexisting wiring harness and you are good to go. Put the savings toward transferable (for a fee) lifetime subscription.