Heat Pumps and Electric Heating - What makes up the "whole System"?

What are the necessary and/or desired components of a split heat pump system? I'm looking at a Trane xl19i 5 ton. Looks like I need the Condenser/compressor outside unit, the inside air handler (air tight) to go in crawl space (which one? two are listed for 5 tons), the line set, and thermostat. What about the inside "air coil" and the "whole house" air handler filter, and which filter medium is recommended. No allergies except spring tree pollen which gets everyone for a couple weeks. Man this stuff adds up! The electrical is separate. ALso, what is "dual circuit"? Any thoughts appreciated.

A heat pump system consists of a heat pump (outside unit).An air handler (inside unit).A line set to connect the two .This is how the refrigerent flows from one to the other.Also a thermostat and all corrisponding wire.
As far as filters go,I used a medium pleated throw away filter that I change monthly.There are literally hundreds of different kinds to chose from.You can go cheap with the fiberglass throw aways.Or you can spend alot and get an electronic air cleaner.Also dont forget about humidifiers.Theres digital thermostats.Programmable and non- programmable.There is no end to the amount of options you can add to your hvac system....Its all in what you want and are willing to spend...Good luck....

panhandle, are you thinking about a total reinstall of a existing system, or are you planning this for a new construction?
barry

ps, what part of the country do you live.