Corys in groups of 6 would let you see them act naturally. A lot of people will say I have 2 and they are quite happy which they may be but once you get them in a larger group you will definately notice changes in their behaviour for the better.
As for the tank if you are after low maintenance and slower growth, meaning you want a permanent scape as in a garden which you can keep for year on year then I would suggest non CO2 and low light is the way forward for you.
As a quick guide the plants require a few things to grow: Light, Carbon and Nutrient. The whole system is driven by light so the more light you have the faster the plants are driven to grow which then means they need more carbon and more nutrient (NPK = Nitrogen, Phosphate & Potassium.) You don't need an RO system the water although being wuite hard in our farming county is almost perfect for planted aquaria.
People who are after fast growing scapes which they intend to change will more often than not drive the plants to grow fast which means high maintenance and pruning. This is their aim so they don't mind.
So a good substrate topped with sand, light between 1 & 1.5WPG of T8 or 1ish T5, No CO2, Heavy fishload to supply NPK and low light slow growing plants should give you what you are after. This method also requires only siz monthly water changes!!! this is to keep a stable CO2 level from the natural gaseous exchange where tap water would keep boosting the CO2 and unstabilise the level.
Anubias, Crypts, Ferns, Mosses and Nympheae are good for this kind of setup. There are many other low light plants.
I am basically describing my tank here with the exception I am adding ferts and CO2 and driving the tank a little faster. (The one on the right in my sig)
This thread will help you understand a little more about this method:
NON CO2 METHODS
Have a good read because the questions you will ask will mostly be within this thread and it should give you a good idea of what this method involves (or rather doesn't involve)
Andy