I sometimes blend high quality fruit preserves with sour cream as a topping for blintzes using a ratio that's greater on the preserves side than the sour cream side. Caramel sauce works with some cheeses also.
A fruit compote and a quality medium bodied red or white wine.
I wouldn't serve soup, except perhaps for a gazpacho or vichyssoise, with cheese blintzes. Depends on the variety of cheese and the topping. Neither gazpacho nor vichyssoise would pair well with fruit based toppings and fruit compote.
I haven't heard much about cheese blintzes, but they do sound yummy.
What about a 3 mushroom soup or tomato? I think fruit salad sound perfect.
A nice topping for your cheese blitzes could be a pesto based drizzle, or perhaps a zucchini and tomato saute with basil?
Would you tell me are you baking the blintzes? I'd love your recipe.
You could serve some smoked fish and dark breads. I have served a ratatouille or other mixed vegetable casseroles that one could add some white beans for more substance. If you don't serve a mixed vegetable casserole, you could serve a hot or cold vegetable soup. A fruit salad sounds great for dessert. You could also serve some simple vegetable salads like cucumber or shredded carrot salads.
You might find this thread (where someone posed the same question) helpful.
I think that a variety of fresh, seasonal fruit toppings would be nice (eg. raspberry coulis), as well as some sour cream.
If you want a soup, perhaps a cold cherry soup?