I'd say, yes, NWC can be aggressive. Most Cichlids are considered at least ‘semi aggressive.’ But like with every group of fish it depends - different types of species differ in aggression as do the individual personalities within a species. I'm still learning about the different compatibilities among just a small section of SA cichlids – and doing tons of research to make sure I'm making the best choice.
If you want to keep mollies and platys, IMO you need to stick with similar type fish, other live bearers or community fish. Personally I think you’re getting close to your limit in a 10g anyway, but if you have to add more I’d pick a few smaller schooling fish, like tetra.
Are you still considering Malawi for that 10g?