Your scale is way off. For example, your cedar is far too small (It can grow to 35m). and it needs full sun. It's not an understory tree.

I just made it that size to make it a bit easier to visualize, there’s a big open sky over head where it can grow to reach the light

Visualising it that size gives an entirely inaccurate idea. I don't see how that can be at all helpful to you. And it needs 6 - 8 hours of full sun. Growing towards the light would result in a spindly and malformed tree. To get the layered branches you need to have it out in the open. Sadly this one has been limbed up but the natural shape is wide and spreading. Note the height. And the open position.

Scale aside, none of the conifers you list will be happy in that amount of shade - by and large, most conifers are not shade lovers and want full sun to thrive or as close as you can manage. You should be looking at broadleaved evergreens for shade, although yews could work as well for the coniferous element. Otherwise, consider plants like:

Itea

Skimmia

Sweetbox

Leucothoe

Aucuba

Clethra

Fothergilla

Japanese holly

Pieris, azaleas, rhododedrons

most dogwoods

It’s not especially shady, just partial shade, and I expect them to grow to be part of the natural forest canopy

Partial shade is still shade. And those conifers do not grow naturally under those conditions, so not likely to "grow to be part of the natural forest canopy".

How could you possibly think otherwise?

Grand fir grows in dense huge rainforests and naturally grows in the forest understory when young. Balsam fir also grows in swamps in the northeastern US under dense hardwoods when young. They’re shade tolerant when young but then grow to reach the light.

Sounds as if you've already decided. By all means try it. But it'll be quite a costly experiment.

Back to the Cedar. They are not the kind of conifer that grows in dense stands. They are best seen as beautiful stand alone specimens with plenty of clear space around them. I don't see the point if planting an expensive specimen tree in a crowded woodland only for it to struggle. It would be a waste in every way. You might just as well put in any cheap uninteresting conifer.

I believe you are operating under some false perceptions. Grand fir's native range is my area of the world and it most definitely does not "grow in dense huge rainforests". The Balsam fir is arguably more shade tolerant but will struggle in anything more than light or dappled shade.

Since you seem to like to ask questions and then follow your initial path regardless of the responses, go ahead and plant whatever conifers you want. But if I were you, I'd focus on other shrubs to carry the load or your "part shade" garden is going to look pretty darn empty.

“I’ve kind of got the right side down now but what about the left?” This makes no sense to me.

You appear to have one large area divided in halves by a walkway. One WHOLE unit. Therefore, the sides should be planted similarly. Not exactly, of course, but very much the same. IMO.

Yeah, I kind of am leaning towards our native hemlock instead of the cedar now, I think it matches the woodland look better anyway.

It’s hard to give advice without more context. Where is this path leading to/ from, and where is it in relation to your house? What hours of the day get sunlight in this area? I think you said you’re located near the Great Lakes— what specific region/ state are you in?

It gets partial sun and in the afternoon, the area with the sky gets sunny. It will be in relation to the pathway from the deck to the main yard and will make sense, I just have to move a tree seedling I have there. I am in Aurora, OH which is in northeast Ohio near the Great Lakes in the snowbelt. We are right on the border between zone 6a and zone 6b and relatively close to zone 7a. Winters almost never get below -10, so we are a reliably zone 6 climate. Some winters don’t get below zero so I’d say we’re in between a zone 6a and zone 6b. Many odd marginal small plants survive winter from our intense snow and get essentially buried until springtime. I have Callas coming up from last year that I completely forgot to dig up.

And although we’re a little farther inland to get the intense moderation the coastal areas get, we still get a bit of it which helps in the winter, and we are pretty high elevation for Ohio standards, my yard sits at around 1200 feet in elevation which helps nights in the summer time cool off and makes the summer temperatures a bit cooler.

Are hemlocks native to your area susceptible to wooly adelgid?

Nope, not really. Haven’t seen a single tree with wooly adelgid around here in the wild or in anyone’s yard. Hemlocks however are much more sporadic and few and far between compared to areas like southern Appalachia or New England so I don’t think the insect really gets around as easily. They’re a little more uncommon in the wild, however I definitely still see them.