1) You can't get demerit points from a red light camera. You only get points if an officer gives you a ticket for running the red. I don't know how likely it is that they'd reduce your fine, others here can attest to that better than I can.
2) Not sure what you mean. I've never had a red light camera ticket (so I could be wrong here), but on a normal ticket option 3 means you're pleading not guilty, and you have to go to the courts to set a trial date. If you chose to plead guilty and pay the fine (option one on every ticket I've ever seen), then you just send the amount you owe in, or do it online with a credit card. You don't go to court or anything.
3) Read the forum. I'm in the process of dealing with a red light ticket myself, there's lots of info here, you just have to look around a bit. I would, however, advise that you don't use the excuse that you couldn't see the light due to the bus blocking you. You *technically* should of slowed down and proceeded with caution, if you could not see the lights. (Not trying to judge you, just pointing out that the courts probably won't be sympathetic to you).
Red light camera tickets are difficult to beat (from what I've read and heard). Not impossible though, I do have one buddy that beat his, but there were extenuating circumstances (weather).