Just goes to show that what you find on the web may or may not be true! For us, the old gardening tale is that farmer's plant their spring gardens on Good Friday. Now sometimes that works out but other times it doesn't. Two years ago, we had extremely warm weather early and then Easter weekend we had temps down into the low 20s. Quite a few things got zapped and anything that would have been planted out by the old gardening rule would have been frozen beyond recognition. As far as last average frost days, they are just averages. If I remember correctly, our absolute safe time to plant out to not have to worry about any extremely late frosts is sometime in May. Of course I never wait until then to plant things out--even those things that are not frost hardy. Believe me however, I have been out there at times covering things up if a later than normal frost is called for! LOL

Batchelor button is a good choice because it can take a light frost, and in many parts of 5b the chances of a frost by mid-October are better than slight. I'd add a mix of double calendula -- the old Pacific Beauty mix would be fine. The flowers are much smaller than sunflowers, but they aren't tiny, they cover some of the color range you're looking for and they're very frost hardy. You don't have to start either of these early. I'd wait to start the batchelor's buttons until summer, so they won't exhaust themselves by October. The calendula seem to bloom and bloom. Plant a goodly number of each. You might think of something like a double feverfew to give you a white filler. They're also cold-hardy.

I'm from the Detroit area -- probably close enough. You should plant them as soon as the soil thaws, which is generally some time in mid to late March. If we have even very cold weather after you plant them, and it freezes up again, it won't really hurt them. They'll take a few weeks to germinate anyway. I've read that every day you wait after April 1st to plant them resulted in about a 3% decrease in yield in test plots, since Favas are very, very photoperiodic and will bolt to seed when the daylength is long enough, whether or not the plants are big enough or ready. Favas are fun. Unfortunately, I never get a very large yield out of them -- what usually happens is we have a hot spell just when they bloom, and most of the flowers drop without setting a pod. But, they're very pretty plants, and the tender leaves and shoots can also be used in salads or even as a cooked green.

Unlike most other fall planted bulbs, lilies never go fully dormant. That's typically why they are offered for sale in both the fall and spring. They don't keep well out of the ground so the recommendation is to plant them ASAP. Cold is not really an issue but the state of your soil is. Obviously if the ground is still frozen you can't plant now. You also want to avoid overly wet or saturated soils. But if you can work the soil and it is not excessively wet - lilies want good drainage - plant now. If you can't plant directly into the garden at this time, then I'd suggest planting up in containers, which can then be transfered out into the garden at a more suitable time.