From what I can determine now, the cable housing length is about 41"/105cm. I would add at least 1"/2cm for any mishaps - I already shortened it by 1cm or so due to one. Yes, it goes with other cables through the hoops. There is one sharp upturn to go up the seattube - difficult to make it milder.
See my earlier posts in this thread. The Sunrace cranks mount farther out on the axle than Brompton. My going with the shorter BB axle aims at pulling the Sunrace crankset in, not pushing it out. Yes I have a 2mm spacer on the RH side, but it is inside the BB cup to move the spindle to the left, rather than right, empasizing again. Yes the bike folds fine and neither the inner ring nor chain on the inner ring touches anything. I could presumably move the axle to the left by 1mm more without a problem, but I am not forced here to push it to the wire.
Thanks - I fitted the Shimano Hollowtech ll, (SM-BB-R60) BB - but other Shimano BB's also fit as they are the same size, (119mm) as the Brompton BB, (the newer JIS one) - and used Shimano Alfine cranks with a crank length of 170mm - 5 arm - PCD 130 with a Middleburn Outer Chainring - it fitted the Brompton just fine with no spacers........ and the Chainline with one Chainring was fine.
Looking at developing this based on your experience with the 105 compact changer and the Braze on bracket off ebay