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A standard drywall board is 48" in width. If you are making accurate cuts then you would be able to get 4, 12" pieces out of a board. The drywall should also be lifted off of the floor approximately 1/4" - 1/2".
When the boards are hung and butted up to each other, now is the time to mud the drywall. Lay a thin coat of drywall mud over the seam and then cut the tape and lay it along the mud line and gently press it down. Now go back over the taped line with another thin layer of mud. Let dry.
Feel free to post any follow-up questions you may have.
I would cut the 4 strips and leave the tapered sides to the floor. It is harder to finish a joint that is tapered against a cut. This will leave you butting a cut edge to a cut edge.
If you run a layer of mud along the bottom of the board that will take care of the tapered edge along the bottom.
You do not need a coat of mud underneat the fibertape because it has a sticky back and will adhere to the drywall. The first coat of mud over the fiber tape should be a relatively thick layer, approx. 1/8" to 1/4" thick. This will prevent the tape from showing through the layer of mud.
For a smooth finish, I would run 3 coats at 8", 10" and lastly 12"