Well, as Jay so eleoquently stated, what will this do to your resale value or market value, will someone else want it in their home?
This is all about this.
To cover the doorway, is simple. Take the door off, take the molding off, take the frame off. Take everything off until you get to the bare studs and the drywall.
Now, install a stud on each side of the doorway inside the hole. Run it from top to bottom. Do the same on the other side. Just nail it to the existing stud. what you are doing is creating a lip or something to nail the new drywall to. i am estimating that the door width is 32". Now put another stud dead center.
Now, measure the opening and cut a piece of drywall that size. Place that drywall in the hole and carefully using drywall nails or drywall screws and fasten that bad boy to the studs. Place a fastener every 8 inches.
Now, you have done this on both sides. OK
Now, surely you have dimpled your nails or screws. right?
Now place fiberglass flex tape over the cracks on both sides. Lay on some good quick setting joing compound. trowel this stuff in and make sure it gets in the crack good. Now use a 6 or 8 inch trowel and lay it on again. Wait 1 hour if using 20 minute set and then sand. Lay on some more. do this again for three times.
On your final coat, here is the hard part, you need to match the best of your ability the surrounding texturing. This is hard.
After this is done, lay down your baseboards on both sides and paint all.
Door is in.
now, the half wall.
half walls are terrible because they cannot be securely fastened and wobble allot and get worse with every lean and sit on.
Most half walls do not go from a wall to a wall. This would be good if they could, but they cannot unless you are going to jump over the wall each time. I am sure this is not the case.
Mostly they have openings on each end for access. this is the problem, they have nothing to fasten to. you will have to overcome this problem. I hope that you decide not to go ahead with this wall.
But if you do, just like building any wall, it just does not go to the ceiling. Get a 22 nail gun and fasten the 2x4 to the concrete or if wood floor to that. Then nail another 2x4 on top of that, but first, build your wall with 2x4 every 16 inches on center. This is very important so that the fastening of the drywall is properly done. Now cap this wall with another 2x4. Now with help, stand this wall on top of the 2 x 4 nailed on the floor and screw or nail it down. Now do the drywall job, the tape and bed job, the texturing job, the installation of the top job, the painting, the molding, and there is the wall.