SharePoint 2013 SP1 Installation - Order ?

Hi,

There are many blogs on how to install SP1 on SharePoint 2013. Some of them says that we should install SP1 on the Applications Server first and then WFEs. Others say that the order is not important.

Q1 - Is there a server order to install SharePoint 2013 ?

Q2 - May I update half server one week and second half the week after (and having my farm working correctly in between)

Q3 - SharePoint Server 2013 SP1 contains SharePoint Foundation SP1. Why SharePoint Foundation SP1 still exist, could I deploy only SharePoint Server SP1 package eventhough I have only SharePoint Foundation installed ?

Thank you