I built 2 boardwalks similar to your plans about a decade ago, one being about 2 ft. wide and the other about 3 ft. wide. The whole structure is pressure treated (poison treated) 2 X 4 pine. Over time the boards warp, fade, and need replacement. Toads dig under the edges to set up shop underneath, and tree roaches camp out below also . Snakes go underneath looking for both habitat and lunch. I will not build any others, but instead have had a much better long-term result when just laying down 2" X 24" X 24" concrete blocks sold at Lowe's for about $9. Because there is only a small amount of cement holding the sand and fine gravel together, they will break apart if not handled carefully. When the time comes to rip out the 2 deteriorating boardwalks, the concrete blocks will replace them. The wood may look quite nice when new, but not for long enough. AND..., when regular rainfall soaks into the wood...., and you try walking/jogging across the slick surface, WATCH OUT.

Actually, I want to go sort of the opposite direction. I have a stone pathway now, and want to continue it on in wood.

I get the vermin and rot issue but I'm wanting to keep the wood off the ground by a bit, dunno but i seems to work in parks so I'm still looking into it. Here's a part of what I have:

Have you decided on what you'll do with the wood yet Gnappi? I don't know if maybe glazing over the wood would make it more resistant to rot, but we do get lots of rainfall down here. And do you notice a difference with your fruit trees grow where you removed the grass versus the ones that grow in the grass? I'm thinking of taking up the grass round my fruit trees as well. Your sapodilla looks nice; what do you feed it? :)