For a couple of reasons I stayed home today and have, among other things, been working on the HW system for the garden room. I hit a slight problem, well two really and they are explained in the attached image. Essentially we are using an instantaneous hot water heater like the one @JSHarris uses. to provide HW there are three HW outlets one to the kitchen sink and two in the wet room - basin and shower. I am thinking, now that I have drawn it, I won't need a mixer tap and can rely on the heater to control the water temp. In other posts we have worked out that we can get the temperature we need provided the flow is not to high. I also wondered if having a simple control scheme that prevents water being drawn by the basin taps if there is any flow to the shower, might have value. I have found the bits I need for that but not sure if I am just over thinking this. Any thoughts and / or ideas?
PS the drawing on the left is the physical layout from the floor ducts - under the kitchenette worktop.