Fully grown adult mollies are pretty large by livebearers' standard. Shrimplets will definitely get eaten and smaller adult shrimps will probably fare no better over time. If you want to keep the shrimp colony growing, then I think it's a fish worth avoiding.
Otherwise, like most other...
Can't go wrong with most commonly available varieties of java fern and anhbias, really.
Bear in mind that goldfish LOVE live plants, as in they will likely snack on it and the plants will need to replaced every now and then.
I'd recommend two slighly large schools like
8-12 zebra danios/black skirt tetras
8-12 juliI cories
Or you may like
3 platies (males)
6-8 zebra danios/black skirt tetras
6-8 juliI cories
Those seem to be the most drama-free, beginner friendly out of your whole bunch. What kind of substrate do...
Sounds like a heavily stocked 75g, probably overstocked if all three are fully grown adults. I wouldn't add more. Severums and JDs get pretty big although they tend to be more mild-mannered than the feisty mid-sized convicts.