1) JP is a connector. I usually use screw terminals but you can use anything. the barrier terminal on this page might be good:
https://www.jameco.com/webapp/wcs/s...toreId=10001&catalogId=10001&productId=440858
2) OEG-PCH is the type of relay I used to draw the circuit. Its a fairly cheap relay, I'd recommend a sealed unit. sorry for the confusion.
3) The coil voltage to the spark plugs will be fairly high. Most relays aren't rated for higher voltage. it may well be fine but I don't know. I'd try to switch lower voltage going to the coil.
4) jp2 has 2 connectors the top one goes to +12V, the bottom one goes to the minus terminal (basically 0 but you might think -12V).
5) just about any trim pots will work. those aren't trimmers though. yes, they will work but I was thinking more along the lines of
https://www.jameco.com/webapp/wcs/s...toreId=10001&catalogId=10001&productId=241496
the idea is that you adjust the pulse width and frequency with a screw driver and then never touch them again. Maybe even drop a little nail polish on them the keep them from moving.
You can get everything from radioshack. I prefer mouser but I think Jameco.com is probably a reasonable choice for you - better pictures than mouser, better products than RS and, of course, better prices than RS.