Really need to make a distinction between cool weather plants and warm weather plants.
The cool weather plants include broccoli, cabbage, cauliflower, lettuce, spinach, swiss chard, carrots. They like cool weather, tolerate some snow and frost once hardened off well, and do not like hot weather, tend to bolt (go to seed) or fizzle once it gets hot. They should be in the ground now. Here in zone 6, I planted mine in mid-March and my broccoli has heads on it now. Broccoli planted late tends to go straight to flowers without setting heads.
Warm weather crops includes pretty much everything else, but there are degrees. Tomatoes and peppers don't tolerate frost, and they don't like it really cold, but they can tolerate a bit of cool (nights in the 40's). The things like squash, melons, cucumbers are the last to go out, they like the soil nice and warmed up.
So for RuH... yes if the spinach has been hardened off a bit, get it in the ground ASAP. But for next year, lettuce, spinach, swiss chard, etc really don't need to be started indoors. They are quick-sprouting, fast growing and can be just direct seeded in the ground. Then they are cold hardy from the beginning and don't need to be hardened off. Cucumbers should wait a while yet.
For dmcn... lettuce, spinach, broccoli, brussels sprouts should be in the garden already. Onions are often planted in the fall to over winter and then grow in the spring. All of these (once hardened) will tolerate light frost just fine. Mine got snowed on after they were in the ground.