It would be nice to know what type of flowers your bulbs will produce, since the depth of planting will vary. However, it's alittle early, at least by the climatic standards here in the western U.S. You want the soil temperature to be dropping since, if it's above about 60 degrees F or so you run the risk of the bulbs coning out of dormancy... not a good thing.
I like to wait until after the first frost when I clean up the garden. Here, that's usually late September or early October. I usually just plant them in the in-situ soil with no compost and very little, if any fertilzer.
As far as depth is concerned, I like to plant tulips about 2 inches deeper (say, 6 inches) than I plant crocus or any earlier flowering bulbs. That way, as the crocus or snow drops begin t fade, the tulips come up among the remains and I only have to clean up once...
Best of luck!