The clown loaches would be great with the knife. I've kept them together everytime I've owned a BGK with no problems at all. As far as the cichlids you've chosen, it's a very slim chance of that working out. They would most likely be too aggressive for the knife singly, and even moreso if the two JDs become a breeding pair.
You said earlier that you plan on upgrading to a 180 gallon, right? If you do that, would you also be able to keep the 125 and have two tanks? You could keep the cichlids in the 125 and the knife in the 180. Afterwards, you could stock around each fish in their respective tanks (though the EBJD probably would not tolerate any other fish in the 125 if they became a breeding pair.)
That said, I wouldn't keep any knife fish with a breeding pair of cichlids. They would be too hyper-aggressive for the knife. Cichlids I'd recommend that could work with a BGK as long as they don't form a breeding pair (from my own personal experience) are severums, uarus, and geophagus. Cichlids I haven't tried with a BGK, but I would expect to work would include keyhole cichlids, bolivian rams, and maybe discus. Again, I would only recommend cichlids with a knife fish as long as you don't get a m/f breeding pair.
Personally, I am a severum fanatic. They are my favorite cichlids. Whenever I get rid of the fish in my 300 gallon to start over, I always buy a group of small severums and grow them out in my 55 gallon until I can determine the gender of the cichlids (I actually do this with any group of cichlids I own be it severums, blood-red parrots, geophagus, or uarus). Once I work out whether the fishes are boys or girls, I then choose one gender to keep as a group for my 300 gallon, and I either sell the others or return them to the pet store for store credit. I will never keep a breeding pair of cichlids because of their hyper-aggression. I also include either a clown knife or a BGK everytime I restock my tank.
Another thing you may consider if you are dead set on having the two EBJD is setting up a 75 gallon for just the two of them. If you want to just go with a single EBJD, then I'd say keep it in the 125 and choose tankmates to compliment it. However, even singly, I would not keep a BGK with any JD variant.
Lastly, with regards to the pleco, I had a bristlenose with one of my black ghost knives in the past. They got along well enough, but the pleco was definitely dominant over the knife in that case even when the BGK grew bigger than the pleco. So, choose a pleco with care. I wouldn't get a particularly huge or aggressive species of pleco with a BGK.
