Lighting – Will many weak bulbs be more luminous than one bright one

I'm going to take a wild guess that the previous home owner put the blanks up because they had the same problem and didn't want to fix it. You likely have a short circuit and need to track down where the short is occurring. I'd remove the bulb from the fixture, unhook each of the wires that you connected before, and use a multimeter to test for "continuity" between the wires on each run (e.g. hot to neutral, hot to ground, neutral to ground for the line to the switch, for the light fixture without a bulb, and anywhere else that was previously disconnected). If you don't have continuity with a simple low voltage tester, then the problem could be arcing that only occurs when 120V is applied. Either way, get this fixed before turning the breaker back on with this fixture wired.

First of all, when you read about a "50W LED", it is certainly saying that it outputs the equivalent light of a 50W incandescent light (although that is often a exaggeration). That "50W" LED actually draws less than 10 watts. This means that it draws much less current and emits much less heat, both of which are the factors that typically limit the allowable light in a fixture.

You'd be able to replace a 50/100/150W 3-way with a lower wattage, even if staying with incandescent.

Second, unless the LED light is marked "dimmable", don't try to use it on a dimmer. You may damage the dimmer, light, or both. Even if the light is dimmable, some dimmers will not work well with a low load: a dimmer that works on a 100W light bulb may not work on an equivalent-light-output 13W LED. They make LED/CFL specific dimmers that may work better.

As for the 130V R40, that is probably a "long life" bulb. Running an incandescent at lower than rated voltage extends its life. Therefore, they make 130V bulbs to run longer on 120V. Just use LEDs rated for 120V.

As for your existing florescent lighting, I assume you're talking about the straight tube type. For a fixture that old, it's probably less efficient that newer florescent fixtures or LEDs but still much more efficient than incandescent. This is harder to replace with LEDs, just due to the area covered. There are LED tubes made to replace florescent tubes but they are still expensive and generally require re-wiring the fixture. These are most often used in commercial applications.