Welcome to the forum...Lots of good questions here. Yes PA requires EPA "Qualified" OWF's. An EPA "Certified" OWF is an "incorrect statement". As stated on the EPA website:
http://www.epa.gov/burnwise/owhhlist.html* The wood-burning appliances that are "qualified" under the EPA's Voluntary Hydronic Heater and Fireplace Programs are not "certified" per EPA's Wood Heater New Source Performance Standard.
On the EPA link above, you will find numerous options for your state that are qualified.
The G200 with just a 32" firebox and 140 gallons of water, sounds a bit small to try to heat 6,000 sq ft in a Northeast PA climate.
Physically looking at various models and dealers is a good idea.
As an owner, I am personally partial to my success with the Eclassic gassifiers. Central Boiler had the first EPA qualified furnace "EPA listed on the EPA site in 2008" and has more gasification furnaces in use than any other company. Their current models have had many changes and improvements since that initial model and and are heating powerhouses with 3 different size EPA qualified models available. Don't go cheap and buy something undersize. Sounds like you intend to heat up to 6,000 sq ft of infloor heating. That is a lot of mass to initially heat up and you will need some btu output power to do it.