Put a good amount of sand in your mix.
Don’t stress out the layout, it is not going to last once they start spreading.
Maintenance can be very easy; after leaf drop take out all the old wood and thin the new canes so they are spaced out. If they still end up too bushy, next fall thin them with more space in-between.
And don’t worry about them spreading. I guess mine do but the lawnmower or trimmer takes care of that.
North-south row east-and-west sides receive equal amounts of sun (if east and west horizons are similar). So no dominant spur direction. Staggering primocanes every few inches is a good idea (for small plantings and if you have the time and patience).
I’m in the same boat. Maybe it’s a VA thing. I dug out a bed, amended the soil in fall, built it up, put in 32 plants in spring and mulched on top.
My soil drains well, so I wasn’t worried about root rot. I was worried about the plants drying out so I put in drip irrigation. It’s been very dry, so definitely no root rot, but dry = deer eating everything. 16 of 32 are still alive at the end of summer and they are tiny little things. I’m hoping that they’re growing roots so that next year they grow canes - but time will tell.
This year I grew canefruit in a better draining location on mounds. It worked well except the deer set my canes back significantly. In my experience, in rural VA (esp by wooded areas), anything grown need to be fenced or sprayed down with deer deterrent after rains (which is impossible to keep up on those heavy rain weeks)…or else you can expect deer browsing.
My main orchard has 3D electric fence and it’s worked very well. All other unfenced areas have been heavily browsed by deer.
BTW, it’s time to protect young tree trunks from deer rub now.