We have the black mirror splashback. We love it and it soooo easy to clean

I think your layout is generally good. With a one bedroom it's nice for guests to have access to the ensuite without having to walk through the bedroom. One thing I do notice though is that there is a lot of hallway/storage/circulation space in the center of the building (in the two bedroom portion) that might be better used as living space. You could pretty easily make the ensuite in the one bedroom larger for example. The wash house space seems unnecessarily large to me as well. You could push the wall dividing kitchen from wash house almost all the way back to where the toilet door is in this plan (you'd then have the toilet door open into the wash room to the right from this viewpoint rather than straight ahead). This would leave much more kitchen to porch access, which would be nice.

Should have added, this is the existing layout:

Hi, apologies in advance for the shoddy drawing, I haven't got the mad skills to do it beautifully on the tablet. The big built in is what I wish to keep, I think I can live with moving the smaller one next to the tiny wood stove and moving that stove too. Thank you!!