well, all I can say is, nice vft, fry it under full sun with a water tray...
feeding wise, one or two trap will be enough, leave the rest alone for sun fry
black spot? more likely to be the remaining of the digested foods, this happens to bloodworms that I fed, if it is some sort of black spot bigger than what you fed, could be a form of fungus/pest...cut it off
a master once told me a healthy vft consist of 7 living leaves at once or more and new growth, your's seems to fit the criteria