Bluetooth modules connection of different modules

Hi, I have a question,
I have already know that A v3.0 bluetooth master module can connect with both 3.0 and 2.0 module or earlier ones which is slave,
But my question is,
If my master module is 3.0, can I choose slave module as 4.0? If it is possible, which parameters must be important for me?
My second question is,
Can anyone help me to find smallest bluetooth v2.0 module, it must not have any processor on it.