. it depends what temperature the underfloor heating is running at . it would obviously be better to pick up the pipework before it reaches the underfloor heating manifold.
Well , you could try it . if the temp of the water is low you would need a larger radiator. Its worth a go . if it doesnt quite work then you could always cap it off .
Underfloor heating is so hard to get to work properly. It depends on floor covering , depth of pipe , temp of water etc.
Usually 50. If you increase it , it won't do any harm. Will just increase running costs