Like other classes of hydrangea (aborescens, macrophyla, serrata, paniculata, etc.) various quercifolia cultivars achieve different dimensions in different gardens. Soil, slope, sun/shade, i.e., microclimates in the same USDA climate zones have their (often indeterminate) impact. Best not to expect a too definitive advice respecting the final dimension in your garden. How you prune a plant may be more deteminate than DNA. Look at other local plantings of those quercifolia cultivars most attractive to you (the responsible municipal department may be helpful). Michael Dirr also has a fine book (2004) on hydrangeas, which almost always suggests substantial variety in same zone plant dimensions.

It's too late when you can no longer get a shovel in the ground. Note to above statement: If the air temp is below freezing, don't expose root hairs. If you get really late in the year, mulch well. Yes, leaves can work. or straw. or a lot of other things.

I have gardenia 'Frostproof' that was planted in 2008 and moved in 2011. It has never been protected. Last summer it produced about a dozen fragrant blooms, and so far it looks OK this year. I have several Gelsemium spemperivrens 'Margarita' and the oldest is about 8 years old. It's really nice in that it's one of the very few evergreen flowering vines for zone 6. Masses of yellow trumpet flowers in spring. I also have a winter jasmine, J. nudiflorum, which is definitely hardy in zone 6. The stems are evergreen, and blooms often appear during any brief warm spells from as early as December all through winter and a final big flush of blooms around April. During the summer and fall it leafs out with tiny green leaves. When they fall, they just sort of disappear so not messy, and as I said the stems are green all year. I also have a J. officinale, which has proven hardy for at least 10 years, but seldom blooms. It survives, but doesn't really thrive. Maybe in a very protected spot it would do better.

Dogwoods don't like to have the trunk exposed and - yes - Kousa in particular tends to be low forking - at least in the open (this is true of many other small- or comparatively small-growing kinds of trees also). Plus Kousa is a bark interest tree, when bark interest trees are grown with single trunks the bark effect is not as good. With that fence there the straight lines and full length or nearly full length repetition of some of the plants in these schemes kind of makes the whole look like a billboard. Your best bet might be to follow the paid for design - but using instead one each of four different kinds of trees, chosen to contrast or harmonize with the particular kinds of shrubs that are directly in front of them. Also the whole would look softer and more fully realized if flowering climbers (clematis, honeysuckle, roses...) were trained onto the fence. Again choosing ones that had some kind of specific visual interaction with the shrubs in front of them. Even as comparatively fancy as it is the fence - it is just as fence, after all - still does not have enough interest of its own for a lot of it to be visible. And it is being used in this arrangement as a backdrop. Plus the lattice like style of it seems as though intended to serve as a support for climbing plants. So it looks unfulfilled without anything growing on it.