Here's the plan. The more scary bits are in green.
Great news is that I've had an offer of help from someone who knows how to do this stuff. Power saw, drill press, here I come! This plan may change a bit when I get some expert opinion.
Clean all the junk out of the room; give away big old TV
Figure out what size screws - find the screws.
Charge up the power drills
Find a temporary table or shelf for the Fibre Op cords and stuff.
Bring in the chop saw. Slice off a sliver from the too-long boards
Decide about the angled corners, one board or two
Mark the measurements for placement
Learn how to use the drill press. Practice.
Drill all the holes.
Find a bit of plywood and make missing piece of baseboard.
Sand away the pencil marks, and any other sanding that needs to be done, edges, etc.
Sand baseboard and top board
Place each board; drill hole through masonite; screw and countersink.
Measure for odd size boards around windows and doors.
Practice with table saw.
Cut and install odd-sized boards.
Decide upon what type of molding for the bottom, and how it will be installed.
Buy it, cut it, fasten it on.
Fill all the screw holes with putty or plugs.
Find the chair rail and get more if not enough.
Figure out how to fasten it on, and install it. (Mitres!)
Box cover for cable wire