Gas and Oil Home Heating Furnaces - Central heat/ ac ductwork

I'm putting in central heat & air in a 1200 sq ft house. I'm using a Trane evaporator/furnace that was designed for a 2000 sq ft house. I'm using a 2 ton compressor/condensor. I have downsized the evaporator to match the 2 ton system.
The house is laid out in an 'L' shape with the airhandler located approximately at the angle of the 'L'.
I have some questions regarding the duct work:
* What size should the main trunk line be?
* What size should the lateral lines be going to each outlet?
* Do I need to compensate for outlets that are near the airhandler vs those that are far away by making the closer ones smaller?
* Am I going to have problems with the airhandler that was designed for a 2000 ft house in this 1200ft application.
Such as excessive back pressure because of not having as many outlets. If so should I increase the diameter of the ducts and outlets to compensate?
* Does anyone know of a website that would provide this type information?
Thanks in advance for any help!!
Bob

You need a heat load calculation done. Search: heating and air conditioning heat load calculations. There are people on the web that can do it for about 30bucks. The calculation will give cfm's and sizes.

Over size an A/C system you may drop the temp in the house,but you will never remove the humidity.Have it sized correctly or pay to have it done later.PDF