Your list is about in the right order. I have most of those, with the exception of the Chionanthus and the Hawthorn.

Based on my experiences, the order is:

Witch Hazel (perhaps 'Pallida' or 'Jelena' - suggestions?)
Cornus mas
Forsythia
Amelanchier grandiflora
Eastern Redbud
Cornus florida (I know this starts blooming before the redbud stops most years)
Aronia arbutifolia 'Brilliantissima' (Simultaneous with the dogwood, pretty much)

I don't know about the last two. All of the hawthorns I know of bloom at the same time as the apples and pears, pretty much, which is at the same time as the dogwoods.

Chionanthus virginicus (?)
'Winter King' Hawthorn (?)

And, they all pretty much overlap each other to some extent.

If you want to extend it further, consider a Cornus Kousa for very late spring/early summer bloom (blooms in mid-June here, about 3 weeks after the regular dogwoods are done), and maybe even something like a Hydrangeas or a Stewartia to extend it into the late summer/early fall.

Bloom sequence does not necessarily repeat across the country or climate zones - various factors may influence it:-)

Here's the bloom sequence of the above for my area....YMMV

Witch hazel
Forsythia
Cornus mas
Amelanchier/redbud/hawthorn/Cornus florida
Aronia
Chionanthus

As you can see, things get a little muddy in the middle but there also seems to be a lot of overlap with the 4 grouped together. Depending on weather, these will all tend to bloom in local gardens sometime in April or May. I'd still put the amelanchier first....it's even popped in March.

Thanks, denninmi! Oak leaf hydrangeas and stewartias are on the potential list, as are Viriniga sweetspire, which I believe are summer bloomers. I'm a little nervous about placement of the stewartia, though. This is a south-facing (mostly clay) slope, and I think the stewartias prefer more woodland soil. So I may have to end up putting that one somewhere else, as I hear they're somewhat finicky. We'll see how it goes!

Also, my evergreen screen will include a sweet bay magnolia (mostly evergreen here), and there is a southern magnolia planted by my neighbor, which will be at that end of the evergreens - so those contribute summer bloom.

Gardengal, thanks for your list also. Interesting - would not have thought about sequences varying much - but then I have never gardened out west, and I know that the climates out there are very different from the east in many ways! I often forget just HOW different.

Does anyone have thoughts about number of tree species I can include before it starts looking chaotic? (It's about a 100-120' wide area - I plan on some grouping and clumping of trees, rather than just a row)

In my former garden I had more than dozen different tree or tree-like shrubs in a much smaller area, not to mention a host of smaller shrubs and perennials. Much of it was planted to screen an unsightly view of the neighbors and to provide some degree of privacy but I'll honestly say that it was as much to satisfy my plant collecting urge as well :-) I don't think it looked chaotic - but that's my opinion. I did give pretty close attention to mature sizes and growth habits/rates as well as foliage attributes and flowering sequence so that the plants didn't conflict and looked good in combination. It was a woodland type garden and a lot of different plant types tend to grow together in woodland settings anyway.

If you keep proper design principles in mind when selecting and combining plants (repetition, scale and balance are the biggies), then I believe the only thing that limits the quantity of species is the space available.

I am going for a woodland feel also, to screen a view. But also because I think the flowering trees and colorful foliage and berries will be beautiful against the evergreeens. One reason I wanted to check on bloom sequence and overlap was to make sure there weren't any pink dogwood/redbud type combinations. Ack! I've seen that and it isn't pretty! (Unless maybe one used a white cultivar of redbud...)

So far as balance goes, I'm planning on smaller ornamental trees in front of medium sized evergreens - with large shrubs toward one end. The evergreens are faster growing, but most of the ornamental trees I'm considering seem to be in the slow to medium growth rate. As far as repetition goes, do you think it's best to plant all of one type together, or to scatter them - with small shrubs for example, I could put one here and three there and so forth. Also, before I finally position things, I will have to find winter photos of the trees I'm not so familiar with to see shape and branching patterns.

This is why I have to plan so far ahead! I go into information overload, gathering every bit of data and advice I can - and then months later I'm ready to plant. :- ) We are putting in the evergreens this fall (which I obsessed over for some time) and I wouldn't expect to put in the other trees until early spring, for the most part. Or maybe next fall, even.