Very likely you can. You need to study the venting standards for the equipment as described in the installation manual until you understand them. I would guess that the method you want to use would be among those approved by the manufacturer. Who is going to install this equipment? If you don't understand it, you shouldn't do it. If you are going to have someone else install it, they should be able to show you the method of venting they are going to use and show you where in the manual that method is approved for installation.

The answers to all of your questions depend on your local/state building and fire codes as well as the specific stove you're planning to install as there are some clearance variations. After checking the above, you'll find a world of information at www.hearth.com

As a natural product this should work well if your situation allows for the thickness. What is below your present floor ? Will it handle the added weight ?

I used a Harman P68 pellet stove to heat my entire home last year. Its about 2,600 sq ft. It heated the main house and upstairs easily. The family room we added on is 46 feet from the stove and has 11' ceilings. When its cold we use the oil to warm it up at night then turn it off when we go to bed. I used very little oil. I still heat hot water with the boiler. We run are stove 24/7 with no problems. Its designed for that. The harman has a large ash pan and you can burn about a ton before you have to empty it. I would think you could heat your whole house with the stove depending on the layout. I used about 4.5 tons last year. I bought 5 tons this year at $219.00 a ton. I have to pay a delivery charge but don't have the bill yet. Probably end up being around $235 with delivery. My oil dealer said I use about 1,100 gallons a year. some is used for the hot water but not much i have found. I figure it costs me about $1,200 less a year to heat with the pellets pepending on the price of oil. I figure the stove will pay for its self in 2-3 years. There are other benefits. Not using foreign oil, non polluting, burns a waste product etc that I like. the heat is very comfortable and does not seem to dry out the house like a wood stove. I wish the pellets were around 200 a ton but demand has increased them. Hopefully they won't go higher.