Ok mate hold on hold on! This is too much arithmetic before my morning coffee! Soo this grid is about 2.5 meters, right, center to center, both directions? You can plant a normal size peach and just form it with pruning in that space.
Also using a triangular grid would give more space for each tree compared to a rectangular one. The trees in our garden are planted in a 3-m triangular grid.
Yes it will require more pruning but a dwarf tree it's usually much shorter lived and much more susceptible to environmental shock.
This sound like a long term project. If you look at it that way it's best to not use dwarf trees. I go even further than that. I would plant seeds and then graft the two-year seedling trees. If you would like to save a couple of years then go buy bare root rootstock trees. Any slower growing but not dwarf rootstock for Stone fruit would do.
The main idea is to have the central taproot uninterrupted. Peaches are not usually long lived trees. That is especially true for dwarf varieties. Also any tree with eats evolutionary taproot intact would easily beat in longevity and health any seedling that was moved.
Last spring I pulled a peach seedling from our compost and it had 15 cm root before it made it's second set of leaves. I grew it in a tall narrow 10 liter pot and now at the end of it's second year it has almost 40 cm central root!!! if you can get that from nursery at a reasonable price, that would be your best option.
Another thing that got me Warren as well is that you are planning very low diversity system. At the very least you should get it four types of trees 4 varieties each. You could easily have 6-weeks of cherry harvest and go from high summer well into autumn with some apples and pears.
If you are hell bent on eating 100 and more kilos of peaches, then 8 trees should be enough for your insatiable hunger and the rest should provide the diversity (you can also think of it as accommodating God's plan if you need another reason). Even the garden of Eden had a varied polyculture design!
Another thing that left me scratching my head is is your intention to criss-cross the orchard with the rabbit tractor. I would say it will be better any more productive let alone easier to maintain the system if you use just the lanes. In other words graze just one dimension of the grid.
This would require making rows of comfrey that encompass the trees and would allow for fruit bushes in-between the trees and of course much more comfrey to harvest.
Finally I suppose you're not going to swale that project up, so think about raised drip irrigation. Let me know if you need any help with that.
Ok I kinda lied there, there's so much more to say, maybe it's about time we did a voice chat as I'm without a computer right now and all this typing on the phone requires more beer to calm me afterwards that I'm comfortable drunk! 😜