The Nietzschean Superman is whatever is the best version of You that is possible. Nietzsche's version was his version and if you read his works carefully, you will realize that if you follow Nietzsche in his version of the Superman, you are not the Superman but rather the sheep that he warns for. You have to be your own self. Being "uber" is all about being free and without constraint to be what you are; it is about willpower and unwillingness to be restrained. What this exactly means varies from person to person. For one person it may mean being dominant and powerful, whereas for another it may mean excelling in kindness and love. If you are letting your perception of uber be determined by what Nietzsche says, you are only making Nietzsche spin in his grave because what he is really advocating is for you to makep up your own mind. Nietzsche doesn't want followers, but equals.

Coming back to the post, I think it's perfectly fine to be resentful as an ubermensch! Nietzsche is all about experiencing your feelings and emotions. I don't think an Ubermensch needs to be selfish per se, although this could be a side-effect rather of being unconstrained of what other people think. A true ubermensch would, however, be above petty feelings like greed or material gain. I do not think an ubermensch would care about societal standards at all.