The reason to remove Sulphur heads is not because there are two, it is because they seldom color well in an all-male tank.
Well colors are right for Protomelas splionotus mara rocks and they had that protomelas stripe/marking but I have a felling that they might be hybrids. According to web sites spilonotus max size is 10inch and those guys are 5-6inch. I have them for over a year and some time ago they seem to stop growing. My Capido Borley enter tank after them and he is already 7inches long.Ah the beauty of marketing names. My comment referred to the peacock Aulonocara maylandi. You have haps...lithobates? Spilonotis?
HiI also have a 120 gal. Long tank. I prefer the boxy shape of the 5 foot 120 over the rectangular, thin shape of the 6 foot 125 gallon
Might be a good idea to remove the JD asap. Sooner or later the JD's fins are going to be nipped, or a tankmate is going to suddenly be missing.
I keep a mixed, mostly male African Community. A couple of predator Haps, a few more docile Haps, two Blue Dragons & Ruby Red Peacocks, Red & Blue Zebras, Trewavasae, Zebra Chilumba, Afra, Chailosi & Kenyi. Probably 30 - 35 fish, counting the five Botia loaches.
You have a lot of options with the bigger tank. If you want to add Mbuna into the mix, maybe add a well constructed rock pile.
In the past, I also included a lot of driftwood into the hardscape of my African tanks. Although it looked nice, something about the tannins made the set up look awkward. Once I removed the DW the fish became more active & colorful. My guess is the DW caused a slight drop in PH.
Your new tank looks awsome.