I'm going for the achievement where you get all the endings and I need a little help. I already talked to David and I'm about to go help out Taggart before I head down to the core. I have a few questions...
 
1. There are 4 choices, right?
2. Will I get all the choices assuming I talk to David and Taggart near the end?
3. Without spoiling much, when should I save my game before I get to make my choices?
4. Is it like Fable II where I simply choice something, get the achievement and load it again or is there something else I should know?

1. Yes.
2. Not sure actually. But I'm pretty sure.
3. You can save right in front of the place you make your choice. Hell I think the game even does an auto save.
4. Not entirely sure what you mean. You pick an ending, load, pick another ending ... pick the last remaining ending - get achievement.

1.yes
2.yes they will all be "availible"
3. you will get time to think about all 4 choices before "selecting" one save 
4. to get deus ex machina achievement for all 4 endings in one playthrough i simply saved before my choice, watched said ending and reloaded said save 3 times while picking a different one each time and it popped at the end.

to get deus ex machina achievement for all 4 endings in one playthrough i simply saved before my choice, watched said ending and reloaded said save 3 times while picking a different one each time and it popped at the end.

@DarkTravesty said:

to get deus ex machina achievement for all 4 endings in one playthrough i simply saved before my choice, watched said ending and reloaded said save 3 times while picking a different one each time and it popped at the end.

I know there's something after the credits so I'll watch through once, but do you have to watch the credits all four times or can you just click through them when going for Deus Ex Machina?

i got the achievement once the 4th ending video started playing, so you don't even have to watch up as far as the credits if you don't want to.