The kaffenback has a nice cr-mo fork, I wouldn't waste money on the surly fork it weighs almost as much as the frame you want, you can get tubus fork mounting adapters for 22$ or a u-bolt from the hardware store works perfectly fine as well for mounting certain front racks. Those hope hubs look amazing and I've been eyeing one up for a while. I can't advise on stem angle for a flat bar set-up, if you can grab a used adjustable stem I'd install one of those and just figure it out that way before buying a nice stem.

I would also think about buying the complete kaffenback and selling the wheelset that comes with it, and any other parts you want to swap out... sometimes the parting-out can even finance an upgrade if you can do all the work yourself. I have a build spreadsheet and I've found that small things like grips, rim tape, tubes, cables, etc. really do start to add up on some builds.