So I'm getting ready to build a patio with a flower box on 2 sides. Please let me know if there's a better community for this question. First I'll talk about the patio.
I think I need to have a wood border to the patio to make sure it all stays together, especially because where it's going has a minor slope. I'm hoping to use flagstone and I would like the spaces between the stones to be filled with moss. Where I'm digging up already grows moss naturally so I'm hoping to just save that moss and have the top layer before the stones be dirt and use that moss to fill in the gaps.
For the flower box, I'm thinking I'm going to use some .75"x2'x4' boards, sink them a foot into the ground so they're 3' tall (mostly to keep away groundhogs), then use some 2x4s to stabilize the walls and a few bracers going across. Then fill it with dirt and start planting.
Is there anyone here with enough experience to approve my plan? Am I over engineering or is that a good idea for someone good at being sloppy and who hasn't done this before? Should I fill the bottom of the flower box with rocks or something to save money on dirt? Any changes I should make to my design? I do have a schematic I made if you think that would help make sense of my idea.
Thanks for reading!
Edit: Schematic!

End unit of a townhouse style condo. Should I not bury it at all? But I'd still have to level out the ground because of the slope? Shorten its life by how long? Does that change at all if I'm looking at plywood? I'm aware of the prep and substrates, I just wanted the dirt as the top layer before the stones to support the moss. Or am I that much better off using some kind of square shape and dropping the moss idea?
How much shorter depends on a lot, like moisture content, ground composition, stuff like that so I couldn't say with any precision but I've seen PT wood rot to disintegration in less than a couple years. You could just kick the top of the piece and it just crumbled.
There's options for you if you're set on burying wood-type construction. Take a look at PVC or trex-style decking planks and see if you can design at least your uprights, corners and bottom boards in that material then if you want(for cost, probably) switch to wood when you're a foot off the ground.
Regarding your stone, I understand the moss is a part of your wanted design and I think you can build it in a manner that you could use it. Like I said, just do your best to keep gaps to a minimum and pack as tightly as you can.