New to fishkeeping - tank setup confirmation

[richly2enjoy]

Hello MCA!
I am new to fishkeeping, and having set up a 10 gallon glofish tank for my daughter (and learned lots of things the hard way), I have caught the bug and am diving in.
I am planning an African Malawi tank! 

Here's what we are planning for the new tank:
120 gallon (48x24x24) glass tank

Here's my main question: filtration!
I was originally going to have a 75 gallon tank, which can easily be handled by a Fluval 406, but then the tank got bigger (thankfully before any purchases were made), and now the 406 will not be enough. So would the FX6 be a good choice, or should I have 2 smaller Fluvals (such as 406's or smaller)? The Fx6 would only be 1 canister to maintain and it uses 3 less watts than 2 406's, but the FX6 is kind of a bear to deal with since it's so big!

Also, here is my stocking plan (ideally 1 male a and group of 4 or 5 females for each):
Electric yellows (this is the only must-have as yellow is my favorite color)
Pseudotropheus sp. "acei"

And maybe something else (or doubling up on the others listed above)??
Others I may add in the mix:
Rusties (kind of small)
Red Empress (not so sure since these are bigger and only the males are colorful - and is their diet in line with the others?)

Any other "peaceful" herbivore suggestions of similar size and temperament, yet different genus from Malawi (trying to avoid hybridization)?

Unfortunately one of my early favorites has left the running as it is incompatible: the Blue Dolphin c. moorii. Soooo pretty!

No hurry as I am taking my time to do this right. Will be looking for rocks soon. Planning a fishless cycle.
Well thanks for your input and comments!

[cranialdisturbance]

Electric yellows,  P. Acei, Red Empress, and C. Moori can all eat the same food. Something like New Life Spectrum. You could throw in a little extra veggie flake. My Moorii have been eating the canned green beans I throw in my tank for my plecos.

[richly2enjoy]

Ooooo! That gives me some hope on the blue dolphin!
Another reason I originally nixed the blue dolphin was tank size, but I think this tank (48x24x24) would technically be large enough (?) for one. I am planning to put in a million rocks, so would there be enough swimming room for a giant (10" when grown) blue dolphin?

Also, most people do not recommend mixing haps and mbuna... so was going by this advice.

I have already purchased and frozen (long story) some NLS veggie/algae type 2 mm sinking pellets, and am excited for this project to be complete so I can watch the fish!

[Regalblue]

Welcome to the forum.

I'd go with Yellow Labs, acei & Rustys.  Call around to local landscape yards & find lacerock.  Pile the lacerock to to top, add the fish, sit back & enjoy.

[mibwb]

Welcome aboard....you'll get plenty of help and advice here....a 120 gal seems big but once you get some hardscape and some fish in there it shrinks... just remember, plan ahead, ask questions and come up for air...so you can enjoy the hobby.

[jcunningham0295]

Welcome to the forum.  I always love setting up new tanks.