In a 150 cm tank, I recommend 15-20 Hyphessobrycon erythrostigma, the bleeding heart, because they grow large while Platydoras armatulus, the catfish, can sometimes eat its tankmates.
I recommend that you plant at least a couple of groves of Vallis because it won't really restrict swimming space, but will make all the fish feel more secure and that means that you're more likely to see the nocturnal catfish out during the day.