This would probably be my first trial circuit for a transistor.
The resistors could probably be 1/4 watt without any serious problems, but 1/2 watt resistors are more robust overall, especially if you get cheap ones from China.
There is a pretty wide range of resistor values that would work for either resistor, so the exact value is not critical.
The transistor is typically rated for somewhere in the 0.5 amp range, but that is if its open to ambient air or has a fan on it. If it's buried in a silicone bubble, it's probably only safe to about .1 amp. It would probably work up to .3 amp, but its life might get shortened.
A single LED shouldn't take anywhere near those values, though. Old school LEDS would be somewhere around 0.02 to 0.03 amp. Modern indicator LEDs might take more, so make sure they don't take some insane amount like 0.3 amp or higher.
I tried to find the tach you are using, but I can't find the exact color combo you have. It looks like the closest one I can find has a high-beam indicator. Are you using that as the neutral indicator? (If so, then that is probably not configurable for a switched ground.)
I'll see if I can find any links to parts. Obviously, you will probably want more than 1 of each, especially since they are almost free.
www.jameco.com/z/PN2907A-Major-Brands-Tr...JT-TO-92_178520.html
Jameco appears to require a large minimum for 1/2 watt, 680 ohm resistors. R1 can definitely be 1/4 watt.
www.jameco.com/z/CF1-4W681JRC-Resistor-C...-Watt-5-_690822.html
www.jameco.com/z/CF1-2W222JRC-Resistor-C...-Watt-5-_661589.html
You can probably just solder this leg to leg, and then put it in a blob of 100% silicone caulk. Make sure it is 100% silicone, otherwise it will conduct. Absolutely no latex.
Test it first before siliconing.
The silicone should not be too thick so it can dissipate some heat, but make sure it's all covered for the sake of electrical insulation and water-tightness (any ambient moisture will make the solder flux corrosive over the course of years).