What type of rootstocks (standard, semi-dwarf, dwarf) are being used in this mini method?

How many fruiting plants are you trying to crowd into how big an area?

Answers to that could result in insightful replies.

Crowding fruiting plants together can require more pruning. They will yield more fruit in full sun rather than when shading each other. I don't know if dwarfing rootstocks result in shorter plant lifetimes compared to standard roots.

The grower of a mini backyard orchard may expect smaller crops of a larger variety of fruit, kind of a sampler orchard. Most people cannot use more than 50 pounds of any single fruit for their own annual uses anyway.

Take a look at the info on Backyard Orchard Culture in the link below for Dave Wilson's Nursery. I had great success with the method when I lived in Southern California, but in the PNW, not as much. Perhaps only two trees close together would work, and be sure that they pollinate each other and grow at the same rate. Otherwise, one will take over.

Here is a link that might be useful: Backyard Orchard Culture

My version of backyard orchard culture was plant multiple varieties, keep them pruned short enough that I don't need a ladder, prune each tree so the center is open to sunshine. It has worked nicely for sweet cherries, figs, plums, in town in Vancouver WA.

I tried genetic dwarf peaches but they get massive peach leaf curl, and I gave up on those.

Summer pruning is a weekend project for me, sometimes 2 weekends. It does keep the trees small.

I did not do the 3 trees in one hole method, because we get a lot less sunshine than the California yards where this method was developed.

This sort of thing in the PNW works best with apples, that do have truly dwarfing rootstocks, and are not disease prone. Stone fruits... forget it here in the land of fungal disease. Keeping them pruned down to size and disease-free is a nightmare.

I had several apple trees for awhile. Then they had apple maggots for two years in a row so I cut them down and pulled them up. Yeah, I know I could have sprayed, but knowing me I would have missed the correct time and I'm just not into a lot of spraying, insecticidal or fungal. By the time you do the pruning and spraying, plus taking up the room to grow them, it's just easier for me to buy them in the store or buy them by the box alongside the road when they're in season.
Same with stone fruits, too much trouble....and I like to grow things!
Mike...My orchard is at Safeway.