Firstly, I'm going to let you kind people into a secret, Ready? I got DAO about... 3 days ago, so go easy on the scrub please 
Secondly (I'm going to assume that because this game is now 6 years old-ish, that people know enough about the end to not get butt hurt when I don't spoiler stuff, that said if you do dislike me doing this, or don't want to know, stop reading now) The question, I've yet to get to the ending part, I'm a F/Warden and my Li is Leliana, should I
1) Get Alistair to become king, and then sacrifice Loghain to the Archdemon,
2) Kill Logain and sacrifice Alistair to the Archdemon
3) have you kind people tell me that there is a way to have a god baby with Morrigan even though she and Alistair are not my Li
4) have you kind people tell me that there is a "better" ending than the previous 3, and I do know about the "Ultimate Sacrifice" ending, I'll be honest and say for this playthrough I don't want to do that.
Not sure if it makes any difference but I'm on PC and Human, not Elven or Dwarven.
Also please say if there is any knock on effects in DA2 and Inquisitions, when doing any of the choice, as I've not looked into that.
Thanks
- Gear
Nicely thought out questions. I'll try to answer them as honestly and thoroughly as I can. Spoilers follow.
Firstly, just remember there is no 'right or wrong' way to play, so enjoy the story you create. 
1. This ending is ONLY possible if you harden Alistair beforehand, and force him to marry Anora (whereupon he will leave your group permanently) and force Loghain to do the Joining. He will survive, protected by Plot Armor. Alistair cannot solo rule and spare Loghain, you will need Anora to be his "Check" on that plot device.
2. This I have done a couple of times: Fair warning however, in terms of storytelling, the Warden Commander/Redeemer endings are both weak in terms of satisfaction at the end compared to the other two. Yes, Loghain gets to make up for a lot of his mistakes by 'redeeming' himself and killing the archdemon, but there is no funeral for either and neither is mentioned beyond one single line from NPCs. TBH both endings pissed me off royally because of the lack of emotional impact the sacrifice made on the story. US was a much more satisfying ending because then you get to see the impact your sacrifice makes on a grateful nation (and the people who loved your warden).
3. Being female won't prevent you from doing the DR. Get Loghain (his approval doesn't even have to be that high) or Alistair (who can be hardened or not--though I think hardened is easier to convince--and high persuade/friendship helps) to do it. The game is designed so even females who lose Alistair at the Landsmeet can manage to do the DR ending with minimal effort.
4. See 2 above on my opinions regarding this--your opinion may vary. As I said, there is no 'right or wrong' way to play.
As for impact in future games. So far, your warden doesn't show up in DA2 at all, though there is some mention of him/her, especially if he/she is ruler, an Amell or a Mahariel. Those three origins get the most mention and still it's extremely small. Alistair will have a cameo in both games, regardless of King/Warden status, voiced by Steve Valentine. Certain quests will pop up in DA2 depending on who survived Origins, what choices you made in the game, but otherwise little impact. As for Inquisition, your warden isn't in that one either, even less of a presence in fact, though some NPCs with the right dialogue options will mention him/her.
Significant Inquisition spoiler below:
And remember, have fun and welcome to the Dragon Age!