The oatcake recipes I'm familiar with are usually about 1/2 wheat flour, so that may be tricky as a starter (starting with pure oats tends to produce thick oatmeal rather than a dough).
A good tomato soup would be good. I like doing it with roasted onions and tomatoes and some garlic to start, then adding stock and simmering, then pureeing, and using just a bit of heavy cream at the end.
Stroganoff sounds good, and would also pair well with mashed potatoes or rice, so you don't have to worry about how gluten free noodles will cook up. Be careful to note that Worcestershire sauce (a common ingredient) is not vegetarian, and sour cream is not always vegetarian (low fat versions sometimes include gelatin). You'll need a good vegetable stock as the base, though.
I'd be tempted to include some dried shiitakes in the mushroom mix - start with small ones (about two inches across or so), soak in warm water, then slice. Then you can save the soaking water to use as part of the vegetable broth for the stroganoff.
The green salad would pair well with the stroganoff, and act as a balance for its richness, and I think a fruit tart would go well to finish.
