I have no idea why you put this in the EW Civic/CR-X forum.
As for your questions...
1.) Stop and Go Traffic - It depends on how "stop and go" it is. If traffic is crawling but you're never really stopped much (like a traffic jam on the freeway for example), then you could probably just keep it in second and use first occasionally. If you're in town going from light to light (i.e., you're actually stopping and sitting) then you probably need go through all the motions (i.e. back to first when you stop, go through the gears, repeat).
2.) Coasting - What's your question here? Are you just asking how to maintain a steady speed? Put it in the gear you want and keep your foot on the gas. If you're talking about coasting with your foot off the gas, then just do it. You don't need to be in or out of any specific gear. When you're ready to accelerate again, THEN you put it in the proper gear.
3.) Down-Shifting - Times that you would want to downshift include engine braking (rather then stomping on the brakes to slow down, put the car in a lower gear and get off the gas), if you're crusing and you want to accelerate (this will depend on your RPMS, if they're fairly low and you want to accelerate quickly then you'll want to downshift), and when you've slowed down using your brakes and you now want to cruise or accelerate again (pick the proper gear depending on your speed, RPMs, what you want to do next, etc.).
4.) How to Down-Shift - Press the clutch in, select the gear you want, press the clutch out. That's it. You don't need to gas it if you don't want to. If you want to haul ass then you're going to want to get on the gas, but it's not required to execute a proper downshift.
Just go somewhere that's not busy (parking lot, neighborhood, backroads, etc.) and practice until you get the hang of it...