I am learning more & more every day, it is pure pleasure
Good for you. As reyalp said, this is a big project.
Who can I check if camera support temp sensor ?
You need to look up each camera's specs. For Canon P&S cameras, if it uses convertinal AA batteries then it does not support temp sensor. If it use a custom Li battery it almost certainly does. For example, here's where you find informaiton on the A1400 :http://www.usa.canon.com/cusa/support/consumer/digital_cameras/powershot_a_series/powershot_a1400#Specifications
The batteries with temp sensors start with the model number : NB- Here's some pictures : http://bit.ly/SvssKw
Here's a example of a "dummy battery" used to implement the 3rd terminal temperature sensor switch : http://i.imgur.com/M3oQTGB.jpg
I saw that nafraf used Canon A810 which doesnt have Li Batt , it uses 2xAA battery
How it is possible to trigger caemra withh AA (not talking about software triggering)
Nafraf's system is a commercial product - he has elected not to share too many details about the implementation. However, I believe he is not using temp sensor triggering (that came after he built his system) and just used the convectional USB remote. I've already provided you a link for that.
Shall I need special script / code to trigger the camera using temp sensor?
The temperture sensor trigger code is available for any Canon P&S camera that will support it but it may require a custom build. It is currently only released by default for cameras that have been tested. All it takes is someone willing to test a camera model for us to release other models.
How can I enable/disable the USB remote functionality (from pc ) so that PTP communications can be used interchangably with CHDK USB remote 5V sync?
There is a simple mod posted that will allow this to work : http://chdk.setepontos.com/index.php?topic=8769.msg105488#msg105488
Incidentally, there is a nice diagram of multicam wiring here : http://chdk.setepontos.com/index.php?topic=8769.msg105464#msg105464