Incrediball or any of the arborescens hydrangeas will not tolerate full sun - you want to stick with the paniculatas, like Little Lime. They are the most sun tolerant. Little Lime should hit 3-5'....the less pruning you involve, the larger end of the scale is more likely.

My little limes that I planted late last summer in full sun are already 4ft high. I have 101 hydrangeas and little lime is one of my favorites. The blooms are so lime and the shrub is covered in them.
I love the look of hydrangea and boxwood. I just did the same foundation planting for a friend but because her windows are higher I did Limelight and boxwood. It came out great.
You might want to go with a smaller boxwood like Justin Brouwers. Just a thought. Either way it will look great. Just amend the entire area before you plant rather than do individual holes.
Good luck :)

Thank you for the info! Green Gardens, I'll look at the Justin Brouwers, as you suggest.

I have a new twist to my planting plans - The city tree in front of my house appears to have a disease. I suspect verticillium wilt, but the city can't come out to confirm for perhaps a month.

My new shrubs would be susceptible to catching the wilt, from what I have read online. How likely is this to happen and would it be smarter to wait until I know which disease the poor Maple is harboring?

I'm not sure if the new plantings could easily catch the disease but it couldn't hurt to wait a month. Fall planting is ideal. Not only is it perfect weather for planting but most nurseries run sales. I'd start getting the bed these are going in ready. Add compost and amendments. Get the soil in top shape, remove any rocks that might be there and then when the time comes it will be easy to plant. (Around my area every time you dig a hole you get field stone).