Generally Fall is a great time to transplant plants. Plants are less likely to be burned by the summer sun, more likely to concentrate on root growth if the air temperature is cold. If the plants are dormant, digging them up traumatizes them less.

Most common varieties of milkweed need cold stratification, so Fall is a great time to plant them. (Some tropical or domesticated varieties can be planted in Spring).

Commercial sunflowers...like the big ones that produce seeds we eat...should probably be planted in the Spring. Most crops have been bred to NOT require stratification and start growing when you plant them. Since they are annuals, they would start growing and get killed by the cold before they flower.

You generally can't plant seeds in mulch...that's part of what mulch is for. Seeds on the surface can't reach the dirt with their roots before they run out of stored energy. Seeds beneath the mulch may have trouble reaching the sun before they run out of stored energy.

I agree, fall is a good time to transplant especially in zone 7. The best time is before you expect rain and on a cloudy day. Water them in well at the time of transplanting especially if rain is not expected. Most plants will develop a good root system over winter and be established when spring arrives giving you a jumpstart. Cutting back first often makes plants easier to handle and since you are wanting to concentrate on root growth, its fine and sometimes best to cut back.

If a plant is marginally hardy however, I would not cut it back until spring and wait to transplant it in spring.

Some plants resent being moved at all so you might have some losses. When a plant falls into this category, I wait until its fully dormant to move it if I absolutely must. Other plants could care less, seem not to notice and can be moved any time. Its a matter of trial and error sometimes.

I plant most hardy annual seeds in fall and definitely the ones needing cold stratification. Perennials are best sown in fall as well most of the time. You can look each type up. Seeds that birds enjoy eating like sunflower seed would be be better planted in late winter or spring. Many hardy annuals will germinate in fall and stay as a small rosette during winter and be well set to take off in spring. Often you just have to use common sense and think how nature sows seed for any given plant. If seeds fall to the ground in fall, its a good time to plant which is what happens in nature.

If a seed is large, its best to bury it about the depth of the seed size while fine seed is best raked in or barely covered. You might want to mark certain seeds. I always think I will remember where I planted something but I never do.

Native plants often grow much larger in a yard or garden setting than they do in their natural habitat because of richer garden soil and regular irrigation. Its very common for people to over plant or to plant them too close and/or end up with a larger plant than anticipated.