Tim, sounds like you have a big project ahead. I'm not sure I can give you all the answers but maybe I can give you something to think about. The biggest problem with a wood floor is changes in humidity and the floors response to it. Wood expands and contracts more across the grain than along the grain. The first thing that I would do is have your lumber kiln dried down to about 6% moisture or so. It should be planned so it is exactly the same thickness and sawed so it is all exactly the same width. Then I would mill a tongue and groove on the edges. If you do this yourself, be sure to use a featherboard on the top and side and watch for changes in your setups with vibration and such. You might want to have this professionally done. Then I would let it sit in your house for a couple of weeks to let it adjust to the moisture content that it is going to be living in.
Now you are ready to lay the floor. You can nail thru the tongue into the subfloor and sink the heads or rent a tool that will do this and is a lot easier to use. If you are laying the floor in the winter, when humidity is low, I would not butt them real tight. In the summer, they will expand and kind of reverse cup. If you lay the floor in the summer when humidity is high you can butt them close.
When it is all down, you will have to sand it flat to get rid of any variation in the boards. You can use about any kind of stain that you like and I was real impressed with Parks Pro Finisher Oil Modified Polyurethane.
Living with your floor will be more of a problem. Since pine is a lot softer than something like oak, kids, pets and wives in high heels should be banished to the barn. How you accomplish this is up to you. Since you probably will not be able to manage this totally, you can plan on refinishing it a lot more often than if it was a harder wood.
Good luck and let us know if you have any more questions. Henry in MI