Is a two-flue chimney necessary?

Hello dear forum members,

we are currently planning the construction of a single-family house. Now the following two questions, which are not entirely clear to us.

1) We want to heat our single-family house as follows: On the one hand with gas, domestic hot water with solar on the roof (if possible and conceivable possibly also for heating water support) and additionally a Swedish stove with water pockets.
-> Now the question: Is a two-flue chimney required for this?

2) It is planned to have underfloor heating on the ground floor and attic floor. Only in the bathroom (GF + AF) a radiator to quickly get a warm bath.
-> Can the two radiators be operated with the same heating circuit, or is a higher flow temperature required here?

Thank you very much for your answers.

Regards
Härtsfelder

2) I also plan to do that. The additional radiators need to run with a higher flow temperature. The underfloor heating manages with a lower flow temperature due to the large surface area. The domestic hot water does have a higher temperature. That should work. I will have a developer explain the details to me next week.