I've got the hub gear version of this. Likewise converted to flat bar with slight sweep and works much better that way IME. The stock cable brakes seem to be awful, so can see myself upgrading at some point.
Nice! I built an older, steel Day One with a disc fork a few months ago. It's similar to what it sounds like you're going for (Genesis with flat bars, hydros, mudguards, big tyres) and I love it. Crap photo but here it is.
picking up one of these second hand for a v tidy price
Think I may switch it to flat bar and upgrade the brakes to hydro. Add mudguards. Maybe a dynamo light set up and the biggest tires I can fit.