I'm stuck in the game's main quest (and with the faction quests) because I'm not sure what the effect of siding with Caesar, for example, will do to the ending I get at the end of the game. In other words, I want to do all the quests in the game that I can, but I'm afraid that if I do NCR quests that I'll be forced to end up with the NCR ending--I'd like to strengthen the NCR but I'd like to have the option of changing my mind if it turns out I don't like them by the end of the game. So, can I get idolized with the NCR and then switch to caesar, or Yes Man, etc., after doing the faction quests? Thanks for any help!

It is not possible to do all quests in the game. Something to do with replayability :thumbsup:.
But know that Yes Man is always an option; while getting Idolized by the NCR will irriversibly make you vilified by the Legion.

Side quests for factions don't affect the story. Well, some do, but they don't control what side you will be on. Main quests determine what faction you side with. For example, when you do enough main quests for Yes Man, you will get this quest called Beware the Wrath of Caesar, which will tell you that any further interaction with Yes Man will ruin your reputation with the Legion. In other words, if you do any other main quest for Yes Man, your rep with the Legion will be lowered.
Although I am not entirely sure that my post is correct, I am thinking I got most of it correct.

There are points of no return, in the main questline. But you can get vilified by or idolized by either faction, and still have a 'get out of jail free' card afterwards. If you are vilified by the legion and idolized by the NCR, doing Benny at The Tops will let you go neutral with them again. If you are vilified by the NCR, you can do the same by talking to their ambassador. But after you've played the 'Benny' card in the main questline, then your faction-affecting choices are more final.