Would like experts' thoughts on the following, replacing my existing a/c and gas furnace, 2200 sq ft tri-level. (I have a 3 ton unit (SEER 10) that keeps up ok now, as does the furnace):

Goodman heat pump with coil to match, res. grade (he said was NOT builder grade, to stay away from those), 13 SEER, 3 ton unit, with heat coils (for possible future use instead of gas), digital thermostat, coupled with a Goodman 115,000 95 efficiency gas furnace. 2 stage. Variable speed blower. Installer is also making some minor (but needed) changes to some duct work and adding a return air to one room.

Price quoted is $6750 total, which includes installing a humidifier that I am providing.

I'm wondering also if the difference in performance between a 13 SEER and a 16 SEER in Indianapolis, IN is great enough to warrant what the installer said would be a jump in price (I don't know how big an increase). Anyone in central Indiana type weather know?

What additional questions should I ask ?

I know some here don't particularly like the Goodman equipment, but the quote includes an additional 10 yr warranty (parts and labor over the whole life) bringing the warranty period to 15 years.