Front tire/disc brake question
The QR system was designed before the advent of modern disc brakes, and as such there are a few peculiarities such as the one you are experiencing.  You should only  worry about rubbing after clamping the QR.

No fork or drop-out is perfectly set.  When you put the wheel in the dropout with the QR open, there likely be a bit of slack in how it fits in the dropout.  This goes away when you tighten the QR.   Depending on how your caliper is set this may make rubbing disappear or if you are unlucky, appear, depending on the final position of the hub relative to the dropout after clamping the QR.

Note that it is also important to properly center the hub in the dropout before closing the QR, otherwise the hub can get positioned off center.  As mentioned this can cause rubbing or worse if you set the caliper when the hub is not properly settled in the hub, you will likely experience rubbing the next time you open and close the QR.

These problems are inherent to combing the QR system with the tighter tolerances demanded by disc brakes.  I suspect this was one of the drivers  behind newer standards such as thru-axels, which should be more consistent when fixing the wheel to the dropout (although I can't confirm as I don't have practical experience with thru-axels yet).  

The practical solution is to carefully center the hub before clamping the QR (e.g., by placing the bike on the ground then opening the QR,  allowing the wheel and hub to center, then clamping the QR).  if you get rubbing the you will likely need to reset the caliper position or back the pads off.   The goal is to set the caliper against a stable wheel position that you can recreate the next time you open and close the QR.