Answer 1

It would not matter which operator you use if the data type is bool. But it will matter when it is a different data type, or when there's another condition right after this one which depends on the previous result, which most of the program flow rely on.

As you know the && will not evaluate the second expression if the first one is false, which is good for performance.

I suggest you use & for operations on bit flags, etc. and && for the logical operations.