Day-trip bike for hefty 40-year-old woman?
Any standard non-racing bike can handle 250 pounds.
If you can handle those maintenance items you're better than the average cyclist.
There's no extra maintenance required for a steel vs aluminum frame -- it takes decades for rust to damage a steel frame even if left outside most of the time.  An aluminum frame, being a softer metal, is somewhat more easily damaged (though the difference is probably negligible in normal conditions).  But aluminum may be 2-3 pounds lighter.
If you're having trouble keeping up with your hubby you probably want something with a few more gears.  An internal gear hub likely is a step in the wrong direction.


I think basically you just want a good quality "hybrid".  The Cannondale Quick 3, for instance, would meet most of your requirements, though there are no doubt a dozen others.  The only real problem with the Quick 3 is that it's got 700C wheels and, depending on your height, you might be better off with a 26" wheel.  Unfortunately, good women's bikes in smaller sizes are a rarity.