Does a new CPU mean new Windows license too?

When Windows is installed, it polls 10 different items and makes a hash based on them.  Normally you can chance 3 of the items (and sometimes up to 5 of them) without the hash failing.  You should be able to change the processor without having to reinstall Windows.  It will detect the change and because it is within the 3 item limit will just create a new hash.

No. Only when you change your Hard Drive or format it (assuming no backups or lose of license).

Most times it is the motherboard only that the license is tied to.  I am sure there are exceptions, but I don't know what they might be.

No!                            

Not necessarily

The license is tied with the motherboard however it is possible to reactivate it when the motherboard is changed.

I swapped motherboards and CPU's and never needed to reinstall the OS. The OS is in the hard drive. I swapped hard drives between computers and they ran fine.

New cpu will handle the existing os with not any problem

you'll get the Windows popup with the toll free number to call.  do that and give them your license number [serial number] --  you won't have to buy a new copy

Only applies if you swap the motherboard.

Only applies if you have an old operating system. 7 can support CPU but everything under you need an new reinstall.