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This will be a little difficult to answer, as your climate zones range from 5 to 8 it seems. If you can include your exact climate zone, then I can better help you to find a plant suitable for your area.

There are many things that would suit this. This article will help you get started: https://www.gardeningknowhow.com/garden-how-to/gardening-by-zone/zone-9-10-11/selecting-zone-9-vines.htm

Sure. This article will give you some ideas: https://www.gardeningknowhow.com/garden-how-to/gardening-by-zone/zone-6/evergreen-trees-for-zone-6.htm

Elderberry, Aronia (chokeberry), Clethra (summersweet), Silky and gray dogwood, Virginia sweetspire, Kalmia (laurel), Viburnum dentatum and V. trilobum, spice bush, Northern bayberry, Inkberry, winterberry and possumhaw will tolerate wet soil. Some require acidic soils and may not be appropriate for your agricultural zone. Most azalea and rhododendron require well-drained, damp soil, not wet soil. One exception is swamp azalea. Most plants that like moist soil will suffer root rot in wet soil. May I suggest you conduct a soil percolation test to differentiate moist from wet soil. https://www.todayshomeowner.com/diy-soil-drainage-perk-test-for-your-yard/

You will need to determine the sun density of the window boxes to make the proper selection of plants.

https://www.gardeningknowhow.com/garden-how-to/info/what-is-partial-sunlight.htm

Some possible plants; Sweet Potato Vine, Fiber Optic Grass, Dracaena, White Licorice Plant, Coleus, Frosted Curls,
Summer Snapdragon and Coleus.
Succulents and Sedums make lovely window box displays.

I would suggest a visit to your local garden centers and greenhouse and see the local selections. They often have plantings that can give you a nice idea on mixing plants.

The Farmer's almanac has a good tool for determining what you should plant in your area, and when. This link will take you to this: https://www.almanac.com/gardening/planting-dates/CO