I've seen plenty of BB'd trees dug in mid-summer of up to 6" caliber not skip a beat- this is the kind of work landscape contractors routinely do that have very high-end clientele. Also well funded arboretums. No misting no wilting of leaves as trees look untouched. Trees needn't suffer any stress at all- but boy, the poor people who have to move all that soil do. Misting is for the nursery trade where trees must be moved long distances, I think, and taking enough soil to prevent stress would be prohibitively expensive. For the poster it would seem to be very good advice, however, given his unusual situation. I've moved plenty of dormant 3" caliber apples bare root and they generally recover after a single season (if you remove all flowers and cut back spurs when necessary)- you get much more root going bare root. I've never liked what tree spades do to a root system and you can never take much root even when hand digging and bb-ing

I agree that your success would be limited unless you had the ability to move a very large root system. The time of year is no problem since it is dormant. The problem is that the stress created by seriously damaging the root system would be complicated by winter desiccation. Also, sun stress on a plant on the NW side of a house is minimal. What it really has is wind stress in the winter. If it looks stressed I would give it winter wind protection (either antidesiccant spray or a burlap screen). Also, I would test the soil. Rhododendrons need acid soil. I would also think of fertilizing if there is a lack of vigor. Be cautious, rhododendron don't like too much fertilizer, just enough to restore vigor. They also need well drained soil. If this area is heavy clay or moist, then the plant would be struggling. If you are serious about moving this plant. I would root prune now. That means going around the plant with a spade and cutting down to contain the roots in a space you can include in a root ball when you move it. This will cause the roots to form a more dense mass that can be more easily transplanted. Then next fall or the following spring, the plant would be ready to move. You can transplant a rhododendron any time if you can preserve the integrity of the root ball and water it after moving until the shock of moving has gone. It is just easier to do when the plant is dormant. Here is a link that might be useful: Rhododendron Culture

The typical root system of established trees will extend many times the radius of the canopy, sometimes as much as three or four times. The canopy of a tree is not something that should ever be considered as a 'marker' for tree roots, as it would be limiting, indeed. However, healthy trees can be removed with most of that root system severed, because when transplanted properly into a good site, root regenerate rapidly. Field-grown (professionally grown) trees are managed in such a way to limit their root development into the surrounding territory too much, but even at that, up to 90% of the roots can be left in the field after digging. No attempt is made to get 'as much of the root system as possible'. For one, the trees would weigh several tons! Anyway, a much more appropriate measurement to give us is the diameter of the trunk, probably at about 4.5 feet up the trunk. That's diameter, not circumference. The ideal way to transplant trees of this size would probably be with a tree spade. The actual size of the tree (in diameter) would indicate what size spade. Tree spades cut the roots sharply, remove the ball from the ground with very little damage to the crown and root ball, and will also move the tree for you. By the way, with the proper measurements, I can probably estimate how much the tree and root ball will weigh, give or take a couple of hundred pounds. Tree spades 'can' be used to dig the hole, too, but the operator might need to be ordered to dig it three or more times as wide than he is used to doing. This is probably the ideal time of year for you to transplant. Do NOT do any top pruning prior to the procedure. The foliage is the energy source that will enable the tree to produce new roots rapidly. Also, plant hormones in the branch tips trigger root development, as well. If you prune the top, then the tree is forced to concentrate that essential energy from the leaf factories away from the roots. Thus, top pruning to compensate for root loss is a myth. As the previous person mentioned, plant only into native soil without any amendments at all. Again, the hole should be at least three or more times wider than the root ball but NO DEEPER! As a matter of fact, the hole can be a few inches more shallow so that your tree sits a bit higher than the surrounding grade. I'm not a fan of the Super Thrive, but I know a lot of people who are. It can't hurt, at least! Be sure to avoid fertilization at this time. All your trees will need is water, sunlight, and time. By the way, the larger the tree, the more difficult it is for the tree. That's why we need that measurement. I can estimate how many months it will take for your tree to become properly established. Questions? Confused? Let me know!

Trees from seed might be a little ambitious for major results anytime soon - I get regular volunteers from my spruce trees, and some from sugar maples but have no idea how long the seed might have been in the ground before germinating and becoming a "real" transplantable tree. It's doubtful they will sprout and grow with the same speed as, say, a package of annual flowers. For your purposes, maybe whatever money and effort you want to spend would get you farther at Menard's or any of the big boxes - Menard's especially always has a big supply of Black Hills Spruce, Austrian Pines, etc. in one gallon sizes on up - last season the BHS and AP's were $5 and change for the gallon size. 5 or 6 trees would at least get you started. I'd pose this question on either/both the Conifers and Tree forums. Be prepared for them to tell you water, water, water is the key, though. (Seems like Iowa generally gets plenty of rain - so far we have too so I don't engage in any regular watering program for anything and stuff thrives assuming ground is prepared properly and the material is planted well.)