Dependent care FSA

if you get a w-2 and your employer sponsors an FSA you can contribute the difference to it subject to any limitations imposed by your employer's plan. since your wages are less than your spouse the max excludable is the $7500 or your earned income whichever is less. 

Yes.  As long as you file a joint tax return (married filing jointly), your overall allowable amount is $7500.  You can divide that between you any way you like.  If you take more than $7500 combined between you, the difference will be added back to your taxable income on your tax return at the end of the year but there is no additional penalty.