Minnnt kind of bigs me up too much haha!
Right so if were going for the 55 thats a good size whats the liters of that just so I know if we are working on US or UK gallons.
Next question, are you 100% on wanting breeding cichlids? American Cichlids can be kept as a community of singletons of unrelated species very successfully - but when you add in a breeding pair it actually throws up more issues than the singleton route.
A great book for reading up and pictures of species is - Pocket Professional Guide to Cichlids by David E. Boruchowitz
A good website is seriouslyfish.com, their knowledge base is great, good info and profiles.
I mention them as we can list off species but none of them will really tick your boxes should you go down the route of a singleton community.
So far as Acaras are concerned there are dozens of species some will be too big for your tank but there is a really nice sellection for you to choose from but I would be cautious of combining them simply because of the risk of hybrids but like I say lots of options
A quick list then - some are rare some more common, seeing you are in Scotland so not sure what your stockists but I know of a few places you could get them from via postage if your not opposed to the idea. The scientific names have recently been revised and I believe it is still on going so not 100% on whats under what name now but it was only in recent months so if you google the names it should still come up.
Right that list...
Blue Acara - actually 3 species that come under that name - Aequidens Pulcher, Aequidens Latifrons (aka Platinum Acara) and Aequidens Coerleous (aka Green Acara) all quite similar just different face markings and underlying highlight colour.
Yellow Acara - Aequidens Metae
Saddle Cichlid - Aequidens Patricki
Some of those may be classed under a group called Andinoacara now but not sure what is what yet really... and not all of them have properly been reclassified. There are other species like A.Diadema but they get a bit big for a 55.
Also worth mentioning are the slightly rarer Acaras that are around and the Dwarfs
The Dwarfs are Laetacaras, Dorsiger and Curviceps - though if you can get the rarer sp.Buckelkopf they are amazing. You also get the larger grouing L.Thayeri which could be tank mates for something like the Blue Acara - not 100% what would happen if you mixed the dwarfs with BAs.
There is also Krobia, Krobia sp. Rio Xingu Red Cheek are becoming more frequent all over the place atm and are a nice little fish I had some for a while but sold them on and wish I had not.
There are a group called Bujurquina but these are quite rare but if you can find them grab them.
There is also the Port Acara group which are pretty nice as well quite easy to find as well but IMO not all of the species are as attractive as above but worth a look.
If you went down the dwarf route you could also consider Keyhole Cichlids as well.
Maybe as an accompaniment to the Acara(s) you could look at Cupid Cichlids they do well as groups and are a great little mid sized cichlid
Hope that helps
Wills