What part of the country are you in? If you are in say Colorado you could get away with a swamp cooler if you are in Arkansas you would need A/C. The benefit to a swamp cooler is constant fresh air blowing the dust and fumes out.
For sizing an A/C unit you need to have a "manual J" calculation done. It is complicated and IMO would be worth paying am HVAC contractor for.
A one ton unit would probably work but without knowing where you are located, what heat generating equipment you have and how many doors/windows you have and how often they are opened it is impossible to know for sure. The last thing you want is an oversized system that cycles all the time and cannot maintain a comfortable humidity level.
