Dreaming up a new tang tank

I think you'd be wasting money on Cyps if you choose to keep Fronts. I think you'd be okay with one or the other and your planned stocklist but I think eventually the Fronts will realize the Cyps taste good. You might get to see a bait ball though.
I've never been able to keep shellies with my Calvus. I've tried adults of several species and they always end up Calvus food. Might just be my fish of course but it's something to think about. You might have success starting everyone as juvies, and as you said, I would stick with females where possible... with everything but the Calvus and Cyps IMO.

I would definitely not plan to put cyps and fronts together. I've read that cyps are part of the natural diet of fronts. They will eat them eventually and that would be sad...
I have had ocellatus shelldwellers in with my adult calvus black congo trio for quite some time without any issues. Aside from the fronts, I think you have a cool mix! If you're set on having the fronts, I'd take a second look at your stocking...

Goes to show you- every fish is an individual. In my case I have a large male Calvus that seems to have an inherent hatred for shellies. On the other hand I have a 6" sexfasciatus that could care less. It's awesome you guys are able to keep them together, I had to go another route in stocking.
I feel your pain with Cyps, Razzo. I'm giving up. At $15 each here my wife has forbade me from trying again.
I've read that featherfins can be very aggressive, but at 7' you should be able to handle some more aggressive fish.

They are/ were gorgeous. I've had the same problem. They never seem to truly acclimate and slowly wither away. Have you tried keeping them in a species- only tank? If I had the disposable income to throw another 10 in the 75 with maybe only a few synos I would totally try it. Mine always seemed stressed and never ate well. Oh well, eh?
I know they're usually not tossed in tanks with shellies, but both N. sexfascitatus and N. tretocephalus can look great in a tank that size. The trets would give you that Front look, but I would stick to one female of each. I went through 3 trets to find a female docile enough to play nice and she's become a fixture for the past 3 years. She's only hit 4" and the sexi ( same age, female, 4 or so yrs ), is at 6". Both are submissive to a 3" S. tinanti male. The tinanti's are interesting but not a true biotope Tang in the sense that they live in the fast moving tributaries. They've mixed well with my stock though.
Again, it's almost always a crap shoot. Some fish are just mean as hell, but my answer has always been to keep the most docile females and they seem to do fine. I just wonder about the Furcifer, but you may be fine with that much space to work with.

I've had pretty good luck with my F1 Cyprichromis Leptosoma Utinta. I've had them for about 1.5 years and have raised about a dozen fry successfully. I was very good about doing about a 20% water change per week. I've kept them with leleupi, cylindricus, o. boops, calvus, and julis without issue. I currently have them in a 75 gallon with multis and a few juli ornatus. I've had a hectic schedule lately and slacked off on water changes, one male got pop eye, which he's recovering nicely from. I did have a cype here and there suddenly die when I tried to do a very large water change., so I've tried to stick with 20% weekly. Raising fry hasn't been easy. I have to watch when the female starts holding, wait about 20 days and net her up to get her to spit the fry. I have to raise those in a separate tank with very frequent water changes as well. In a couple months I put them back in with the adults. I still only have about a 75% survival rate with the fry. I feed NLS with the occasional live or frozen food and spirula flake. They love microworms and they look a little crazy darting around the tank eating "invisible" food.
I bought 8 F1 Cyprichromis Leptosoma Katete a few months back and they are maturing nicely, although looks like the group is heavy in males. I can't wait for those to spawn!
Anyway, just sharing my experience with cyps. I have had some deaths, but find them worth the work.

Ps- the pictures of the ones you had look great!! Sorry for your loss. Perhaps F1's are easier to keep than WC?