Not all plants absorb nitrates some absorb more nitrate than others and some basically don?t absorb any at all. If your goal is nitrate absorbers one plant I?d recommend is water sprite is good for beginners and grows fast would need to be trimmed often. You would still need to do water changes there is basically no way around that. Your substrate and lighting all depends on your budget and he types of plants you want to house as well as how ?advanced? the tank will be, a high tech tank with pressurized co2, regular dosing of fertilizers and high light ofcourse. Or a low tech tank with low light demanding plants. A good quality always helps especially in high tech tanks but if your goal is low tech you don?t exactly need a very nutrient rich substrate you could even have an inert substrate for that matter, just make sure if you have heavy root feeders like amazon Swords for example that you add root tabs. As far as plant filter and fish recommendations I will leave that to others. With snails they will only breed to how many fit the tank for example if they iverbreed and there isn?t enougj nutrient available for them they will die off and all that will be left will be however many snails your feeding/natural food (algae biofilm etc) provides for them. This cycle continues but if there?s not enough food for the snails their population will decrease however everybody has heir own opinion on snails.