Performance of individual calves doesn’t really matter in isolation. It’s profit per ha that matters.
1. Dog collar method appears fairly low labour.
2. Buy them from the same place as original dairy x heifers.
3. See 2.
4. Dairy cross should produce more than enough milk, as long as the cows are fed right. Pasture management will be key.
You don't have any cows, do you? And for a number of reasons, dairy cross suckler cows have all but disappeared. The Holstein and disease risks have seen to that.