Yes, the electoral college chooses our President, but any popular vote Hillary can get adds to the mandate.
Agreed. However, I don't think it means much to GOP leaders. They didn't get the message after 2008, after all. Any loss this cycle is going to be written off as Trump stealing the election from them, and thus there was no mandate because they will say a regular Republican would have won it.
I wouldn't say so. Democrats historically have gotten a comfortable majority of this demographic in every election we have data for. Since 1984, Democrats have gotten >60% of the Hispanic vote in every election except 2004, and it's safe to say at this point that Republicans have essentially forfeited any chance at making inroads with Hispanics for possibly decades. 60% was our floor, more or less, and I'm willing to bet post-Trump it will be somewhere between 65% - 75%.