Add light switch in box with outlet

Over the years, my house has been half re-wired by people with a variety of skill levels. Now I want to add a ceiling fixture and I think I'd like to feed into the old wiring rather than the new (both run near there). Are there any caveats I should be aware of or any requirements on upgrading the wiring? This is for a chandelier taking nine bulbs of up to 60W so it could be a sizeable load (if you want to turn the dining room into a tanning booth :-), but we're starting out with 9x40W and a dimmer. The original wiring is ungrounded black fabric covered from the 1940's that goes to a variety of outlets and light fixtures. I still have to figure out what is on the circuit and whether there is too much load. After pulling up the attic floor boards I found that there had previously been a ceiling fixture nearby and whoever removed it left two junctions in the insulation under the boards. Re-using this wiring for the original purpose also takes care of these buried junctions. This wiring is stapled where apropriate and has nailing protection. I used to try not to think of the "nightmare in the attic" that was the new wiring, although with a few safety fixes, I'm no longer as worried about it as I was. This is a 50A subpanel with 6 fuses. The wiring tends not to be anchored nor have nailing protection, has too many junctions, and is already pretty loaded, but at least it's grounded, it's NM-B, the cables are labelled, and it's not as old. Previous changes seem to be a hodge-podge of replacing just about anything with new wiring. I'd like to work toward a much cleaner layout with circuits that make sense and will eventually catch up to code (probably a never ending story). My strategy has been, if I re-wire outlets, to use new grounded wiring through the floor, since the basement has an open ceiling. Now that I'm adding a ceiling fixture, I'd like to keep it on a circuit with other ceiling fixtures, using the wiring that's already there (assuming it's not too much load), and assuming it is not as vital that it be grounded. What do you think?

I have an electrical outlet with a plug in on the bottom and a flip switch to turn on the disposal. The switch was faulty so we bought a new electrical outlet. There are 2-black, 2-white, 2 ground wires for the outlet. There are 2 brass for the black wires, and 1 silver tab only rather than 2 and 1 more brass. Green screw for the ground. What is the proper way to hook up all of these to each other.