I also agree if you plan on a cichlid community, a smaller Parachromis would work better, managuense can become quite aggressive in medium size tanks like you are planning.
And depending on what type Malagasy cichlid you mean, some are shoaling type, some are not.
If you are thinking Paratilapia,
this genus often works well as a single species, but if you are thinking Paretroplus,
most of these (except nourissatti) are shoaling, working best in a group of 4 or more, and "then" depending on species, may become too large in a shoal in a 150 gal, for any other fish except the Paretroplus shoal at adulthood.
My Paretroplus menerambo easily went from 2" to 15" in less than 2 years and outgrew my 150 gal 6 ft tank.
And though Paretroplus tend not to be aggressive with other cichlids, in too small a tank, will become hyper aggressive, or sometimes when kept as individuals, become sociopathic.
Paretroplus kieneri are relatively smaller ones in the genus and may also be a good choice as far as aggression goes, but still shoals.
Another Madagascan genus is Ptychochromis which may work well in that size tank