I don't think insulating a pot will do much good unless there is a heat source inside the insulation. Insulation slows the transfer of heat from something warm to something cold. Thus if the pot is warm and the air cools, insulation would help slow down the cooling of the pot. However, without a source of heat in the pot, eventually the pot will cool to the surrounding air temperature. If you had a few cold nights to worry about, perhaps the insulation would keep the soil in the pot from ever reaching the air temperature, but it won't keep the pot warm through a long NH winter. insulation would help slow the rate of temperature change in the pot, which I am sure would be good for the roots, but you still might end up with dead plants due to excessively cold roots. i would plant the trees in the ground. Lots of fruit orchards exist on fairly bad soils, so I think your spot will be fine. I find most things, especially long-lived things like trees, are a lot easier to grow in the ground than in a pot.

Agree you don't need potting soil, it does indeed have a different texture. I'm not sold on worm castings, rock dust and mycorrhiza: Worm castings are great compost but any kind of compost can do that job as far as I know. If you have or can get them inexpensively, they sure don't hurt. I have not tried to buy a bag because I make my own compost. Rock dust is what soil is made of, so, if you have soil, you likely have all the trace minerals needed. We had a huge discussion on rock dust here just the other day. If you have done a soil test and find your soil is deficient in a certain mineral - which does happen, just not very often - then you should amend with that mineral. Otherwise you're throwing fruit salad at...fruit salad, and paying for the privilege. As for fungi: they are extremely important for soil and plant health, but they should already be present in soil and compost. Fungi feed on decaying organic matter, so if you have plenty of compost in your soil, you'll have all the fungi you need. But again, it doesn't actually hurt anything. I'm just not convinced it helps if you have otherwise healthy soil.

I would keep in mind the future of the space. The people who owned my house before I bought it put down a gravel (colored stone) walkway. The distance from my driveway to the front entrance way is about 100'. The 1" stones are all over the place... even pushed down through the plastic liner into the ground underneath. They get kicked out of the pathway and just become a general mess. To keep them looking good, I would need to constantly rake them, and add to them every few years. I have removed quite a bit, but it is hard work. And just try weed eating around stones... shin bruises and broken windows! Now I have a combination of large paving stones and wood chips down into the areas where I have had the time to remove the stone. Large paving stones only require re-leveling every few years, and the wood chips are free, and simply decompose, making no serious problems. I would say that small, gravel-sized stones do not make good mulch. So, when you want a different use for the space in 5 - 10 years, you will be glad you used something that broke-down naturally and improved the soil. The other thing is the weed barrier discussed on your other thread. The former owners also used weed barrier around a shrub. The shrub grew up and spread by the roots right through the weed barrier. Weeds grew up from below, and down through the barrier. When I removed the shrub, it was much more difficult to remove the barrier than the shrub! So, from experience... natural mulches, and no weed barrier lol.

Sorry, I think I missed the measurement in your OP. My bad. So.. what do you already have planted in those beds or not? Being able to move those raised beds now or in the fall depends on how much planting in is done already. If you want to walk around them all, your best off making an L configuration. Four boxes across the white fence with walkway around all, and the fifth box making the short of the L where the brown bin currently is. You could also butt them up to make one 20 foot long raised strip with no space between bedsand still pull away from the white fence for walkway on that side. Along the brick wall and chicken wire fence is to set in with natives and maybe a rose or two.