if you want the 125 set up in near future, i'd suggest you do just that, skipping the 55g on the way.
but if you really want an intermediate cichlid tank and don't want to handle the demasoni aggro (BTW
, they are fondly called 'demons' ), i'd suggest ps. acei - a blue fish with yellow/white tails. they have a mild temperament and will occupy the upper region of your tank (pretty rare for a mbuna). i think fishy would vouch for them
clown loaches are a common fixture in ARLC tanks. but put them in at a slightly bigger size (3"+ ) to avoid bullying. they have erectable spines under their eyes, which is why they are left alone. cories would definitely be bullied.
you could try ps. socolfi or ps. saulosi (only dominant male) for the blue effect too...melanochromis johannii / cyaneorhabdos...and...and...