We are partial to older varieties but understand that many (all?) of
these bloom only once a season, which probably won't work for us-at
least not as an exclusive variety. So, what would you plant if you
were me? Finally, would you recommend some quality growers who ship
via mailorder, as well?

I'm not even close to your zone so I can't recommend any specific roses for
you, but I want to clear up the misconception that most of the old roses are
once bloomers. Certainly some of them are, but there are thousands of
varieties that are repeat bloomers.
There are many repuatable online growers. One of the first that comes to mind
for your project is Ashdown Roses, not only do they have great roses, they are
very knowledgeable and willing to share that via a phone call. Uncommon Roses
and Chamblees are two others with good roses and good service.
Good luck with your project, I think it sounds beautiful. I love the cottage
garden look, even though it doesn't fit my ranch style nearly as well as a 100
yo farmhouse.