The main build went really well, couldn't fault MBC Timberframe at all, they did a great job and were super people to deal with. I'd use them again without question.
The issues we've had were mainly unconnected with the build. We're not on mains water and our borehole water supply proved to be problematic. It's sorted now, but it probably took a year to get right and held up a load of other work.
On the plus side, the delay caused by not having water did allow us to get the house pretty much completed inside and get all the systems running, so although we're not quite moved in yet (but pretty close) I do have about a year's worth of knowledge as to how the house performs. The big surprise is that the heating system isn't really needed, but I should have paid more attention to shading on the East elevation, to reduce solar gain. The house tends to get a bit warm on mild days in spring and autumn, when the low sun angle penetrates deeply into the house. No real problem in this regard in mid-summer, as the roof overhang and higher sun angle works to keep the solar gain down.
The house is truly "net energy negative", in that it generates more from the 6.25 kWp PV array than it uses over the course of a year (even allowing for the additional energy needed for hot water once we've moved in), but only by using grid power in winter and exporting a lot in summer.
Overall I'm pretty pleased with the way things have gone, although I made a few mistakes along the way. The hot water system was an issue, as I initially used a 260 litre thermal store, with double thickness insulation and another added layer of 50mm insulation over that, but the waste heat from this still made the adjacent bedroom very hot in summer. Even with all the added insulation the thermal store was still losing around 2.5 kWh per day. The manufacturers spec for these things isn't representative of them being kept hot all day by a PV energy diverter and immersion. I've ripped the thermal store out and fitted a very neat and much smaller phase change material thermal store, a Sunamp PV, and that has extremely low heat losses and seems to work very well. It also takes up a fraction of the space of the old water filled thermal store and weighs a fair bit less, too.
We're not that far from you, maybe an hour to an hour and a half drive, and you're welcome to visit. Hope the above is useful.