plecos are pretty hearty fish and can tolerate higher ph. If you are concerned about the plecos than I would go for CA or SA cichlids, most of them require softer acidic water. I personally think you would be fine.
i would only go with New World cichlids because of the similar water requirements (soft acidic water is ideal), but anything you put in should be on the peaceful side. the only part of themselves that plecos cannot defend is their eyes, and a mean territorial cichlid can pluck an eye very easily, even out of a big plec.
a community of keyholes would be nice, or a load of angels. even though they can be mean, their mouths stay too small to do any damage.
CA cichlids in general come from neutral to moderately hard and alkaline water. Some SA cichlids come from the same kinds of waters (festae for example) while most of the more inland SA species come from soft/acidic to neutral waters.