An insulated concrete slab is better if you need a radon membrane, as beam & block can create voids where the gas will accumulate. Radon gas is a silent killer.
The reason that some people put heaters in bathrooms is that after a shower, you are wet & naked and Evaporative Cooling takes place. If this is a problem, it's better to use infrared heaters/panels. You certainly don't need any UFH, either wet and electric upstairs in a Passive House.
Lewis decking is a good idea, but it won't need UFH.
I wouldn't use air to heat the house, it's a poor way to put heat into the slab. You want a uniform and constant temperature that only UFH can provide. I have visited a certified passive house that didn't have UFH, it's was a disaster.
There are no benefits or advantages in DC light systems in a residential property. LEDs might be DC, but the drivers and controllers are relatively cheap, reliable and available. Overall I2R losses make it inefficient.
In Scotland and in the North of England they often don't use cellular, instead, they connect via a dedicated Long-Range Radio network at 400MHz which travels futher.