#1 → I have yet to check the whole media query, but I will do that in the end as currently I am struck in the mobile version and drop down menu creation. #2 → Yes sir, mostly it is w3c validated.
Did you happen to find out a way by which the search box can be overlapped over the menu when it increases it size with the animation?
The second edited screen shot asks if this is what you want the search field to do if someone clicks in the search field at the width shown above. Do you want the search field to extend and overlay the menu bar like this?