Laying distance 7.5 cm, in the bathroom 5 cm. In the bathroom at least one more wall. All loops between 80 and 100 meters.
Such a rigid rule for laying distances is not necessarily effective. However, the second tip should be followed.
The effective approach is, in the first step, a room-wise heat load calculation (not an estimate). In the second step, based on this calculation, the design of the underfloor heating, with an additional wall heating if needed (usually in the bathrooms). The loops should be as equal in length as possible and not longer than 100 m (pressure loss in the heating loop, hydraulic balancing, pump power of the heating circuit pump).
Furthermore, the heat pump should work directly into the heating circuit, no separating buffer, no combination buffer, no mixing nonsense, no water-based ladder in the bathroom. If there is no exemption for ERR (=EffizienzReduktionsRegler), then it should be equipped with its own fuse to allow it to be easily powered off later. Connection of the heating circuit distributors should be generous (minimize pressure loss before the heating circuit distributor)!
Selection of the heat pump only after the heat load is available. No safety margin for anything.
Whether your heating installer agrees with that is the next question...
Flow30 is a very good tip.
Completely forgot, the pipe diameter of the underfloor heating should also be considered.