Generator transfer switch problems

We are getting ready to remodel our kitchen and would like to remove the soffits. I was surprised to see that they are completely empty, aside from some electrical. It is a 2nd floor condo, but we actually have a small basement. It's very unusual, because only part of the condo sits over our basement. I kind of expected the cables to enter through the floor, but they actually come down from the ceiling. They must run from the panel in the basement up to a central location. From there, I guess they ran them to wherever they needed to go. It looks like they ran the NM through the soffit instead of drilling the top plate. I'm not sure how easy this is to remedy, because there doesn't appear to be a lot of slack. I know they also would be stapled to the studs inside the wall. We're pretty sure that we want 42" cabinets but are also considering 36" with a crown molding above. I'm trying to think of some ideas to reroute the electrical. One thought was that if we used 42" cabinets, we could install junction boxes into the tops of the cabinets/into the ceiling. My understanding is that this would be acceptable and still considered accessible. I know that there are those NM splice kits that are supposedly NM compliant, but I would prefer not to use them. Does anyone have any suggestions? I've posted a picture below. As an aside, I noticed that there is a black cable running through one of the holes. I think it goes to a switch in the kitchen, but we have no idea what it controls. Does anyone know what this could be? Also, what is the purpose of the OSB over the studs? I appreciate any input.

old house, half of the house is old style BX, (the kind with the insulation that falls off when you touch it and doesn't have the ground wire) two prong non grounded outlets. other half was upgraded n the 1960's with a breaker panel and the more modern BX. this half has three prong grounded outlets. one of the old circuits tripped the breaker, would not reset. since i knew from experience, any wire i touched on the old BX while lookng for the short would just cause the insulation to fall off and cause more shorts, i am replacing all of the old BX and two prong outlets with ROMEX and three prong outlets. i am dong it one outlet at a time, testing, then move on. in case i do something wrong it will be a lot easier to find it. the problem. first outlet i put in is a GFCI. the romex going from the GFCI to the next out was left disconnected. ends of wires were not touching. reset breaker, light on GFCI comes on. put volt meter probes in GFCI, GFCI trips. tried testing at the disconnected end of the romex, tripped. disconnected end is where the next outlet goes. is this normal? does the GFCI read the volt meter as a ground fault? or is it having a problem because the next outlet is not connected? or did i do something backwards?