I am in Zone --Maryland outside Annapolis...I have not had a problem with my boxes being blown over where I live but I have read here about it being a problem.
I am planning to move on the water next year and wind is an issue on the water....I will probably be removing some of my casters when I set up boxes at the new house. Always a challenge...but that is what keeps us young
I try to keep as many boxes working all year as possible...in low seasons (late fall/winter) about 10 and all 36 during the summer/prime season.
Spring--(Late Feb-April), Spinach, beets, lettuce, end of my garlic and shallots
Summertime--(May-August), cucumbers, peppers, melons, beans
Fall into Winter--(Sept.-Feb) , beets, broccoli, cauliflower, garlic and shallots planted in November. I overwinter all in late fall and harvest in early Spring.
I also have 3 boxes in berries, 2 blue and had tried elderberries in one this summer, but they floundered and I pulled the one that survived (planted 2 plants)....a shame...I love elderberries so I guess I will ground plant them.
Eb's have made it so much easier to garden for me...I have loved to garden my whole life and don't plan to stop anytime soon...
In zone 5 you could grow lots of things like cole crops and beets...they are among my favorites.
I keep trying to grow beets in the summer....not very successful !!
Keep us posted on your success....