Can I finish Et Tumor, Brute? and still do the NCR ending?

And can I finish Kings' Gambit without making the Legion hostile?

Also can I kill House and report it to Caesar to complete Render unto Caesar while still being able to side with NCR?

http://fallout.gamepedia.com/Don%27t_Tread_on_the_Bear! is active shuts off the NCR quest line. So if you have Don't Tread... active, completing a Legion quest will cut you off from the Republic.

1. No. The NCR will become permanently hostile once you've worked through Render Unto Caesar to the point where you report to Caesar after dealing with the White Glove Society.

2. You can finish King's Gambit without turning the Legion hostile.

3. Yes. You kill House in Render Unto Caesar before you deal with the White Gloves.

So I can't kill Caesar during the surgery and still do the NCR ending.

Also, still wanted to know if completing I Hear You Knocking is what causes the artillery fire at the Hoover Dam battle, or if that happens regardless.

If the Boomers like you, you can have all the Artillery you want. Otherwise, you have to help the Legion with their guns to have the Artillery.

You know I never really noticed that helping any. I heard the bombs, saw the plane, but I was still just going across the dam and killing legionaries.

Note that I lost the NCR support because I got the Boomers support while some of the House Wins quests were active. I went to talk to Mr. House about staying out of the NCR's way (I thought that might be an option) and noticed I could tell him I got the Boomers support. I told him so and it finished a House Wins quest and I lost NCR support perminately. I think if you screw up too much that the Yes Man is the only option left.

That's the way the game's designed - Yes Man is the "fail safe" option.

So I guess you could do the quests for all the smaller factions and just hold off doing NCR or Legion (or Mr. House) until last and you get the most out of the game.

That's what I do. I try to finish as many quests as I can(depending on who I'm siding with) before pissing off the major players

That's the best way to do it if you want to get in the most quests. Wait on torquing off the NCR until the last possible moment, since they're the faction that has (by far) the most side quests.

But yeah, all of the major faction quest lines have trigger points where the other major factions will shut you out and even attack you (NCR and Legion are the only ones that attack). But the main faction quests themselves are pretty much all about dealing with the other factions in one way or another.

That's kind of what really screwed me up last time. I had started some quest at Gomorrah after Bye Bye Love and left it half finished. Then when working for the NCR they told me to check out the Gomorrah, but because I had that quest already half done it really messed me up.