1. What power rating should I get for the resistors, especially R1 and R6, that have direct connections to the battery?
They dissipate very little power so can be 1/4W or smaller.
2. What is R_dummy and "6" beneath it?
That simulates the bulb load so is not on the real circuit.
3. The capacitors, all rated for 13-14 volts (bike's system voltage)? Get non-polar ceramic caps for all?
The ones with the polarity (+) sign are too large (1mF or 1,000μf) for ceramic so they must be electrolytic and rated for at least 25V.
The rest should be ceramic.
4. Regarding U2, which I think is LM339 or LM393, the datasheets of the products all show integrated circuits with about a dozen connections (see example attached). How do I wire it in? Which points are used for this circuit?
There are 2 comparators in the LM393 and 4 comparators in the LM339 but you will only be using one, so you can ignore the others.
Power and ground are pins 3 and 12 in the schematic you referenced.
Using the top left (#1) comparator, the (+) input is pin 5, the (-) input is pin 4, and the output is pin 2.
I forgot to mention that you should buy a socket for whichever comparator you buy.
Make sure you buy the comparator in a DIP package and get the DIP socket with the same number of pins (14-pin for LM339 and 8-pin for the LM393)
5. M1 A06407 - this is a mosfet, right? I couldn't find it Mouser's catalog. Is it written correctly?
Yes, that's just an arbitrary device I had in my model library.
You can use just about any P-MOSFET with sufficient current rating.
This, for example, is cheap and should work.
6. U3 is potentiometer with a 1k maximum, is that right?
Yes, it's a small trimpot with screwdriver adjustment.
Pick one that is 10-25 turn and has the adjustment screw where it's readily accessible.
Note that you should buy at least one or two extra of everything to allow for attrition (goofs).
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