Hey Thunderroad, will attempt to answer your queries :

1. Yes, your correct. If you wish, you could just stay in transit and hang out in the arport itself for the duration of your transit. Immigration shouldn't be a problem should you have to re-enter the airport. Queues are not massive. Although dining options are rather limited in the airport. A good option nearby is the 'Taj Airport Garden Hotel'

2. Not sure about access to lounges, but since your proceeding onward on a CX flight, am sure there should be a codeshare for lounge access in CMB.

3. I think within the transit area, they have some rooms where one can crash out for a few hours and there are shower facilites attached to the same as well. (Not sure of the rates)

4. Not too familiar with the requested regions, hence can’t suggest

5. I enquired on the same once, while in a similar predicament. Apparently there’s some ‘customs bonded storage’ facility. From what I gathered there’s a bit of paper work to be done for the same and I guess it does function like a left luggage service of sorts

6. Yes, taxis are available from the airport

7. Not all all, considering you have 10 hours to spare. I would recommend doing a meal at the Mt. Lavinia Hotel. http://www.mountlaviniahotel.com
Excellent heritage type hotel with stunning vistas of the sea. They have a lovely dining area with lovely views and good food. Time wise would be the same, either getting to The Galle Face or Mount Lavinia. Galle Face being in town, you guys could spend time in town as well, apart from the meal at the hotel. Not much to do in the Mt. Lavinia area apart from the hotel itself. But in my opinion, the hotel more than makes up for this. Running time by taxi from the city to the airport, or vice vera, Maximum : 1 hour. Have done this run at varying times of day and it never has breached the 1 hour mark.

Hope this helps on some level..