To answer some of the questions (thanks to Banthracis and CrazyElectron for pitching in):
1. Entrenchment kind of stole your thunder with the whole "starbase" idea. Do you intend to keep outposts as an option in Last Stand? Or have you varied their functionality to avoid redundancy?
The new races will have Starbases (they will not have static superweapons, that's what Titans replace). Only they're called Citadels and are much more expensive and powerful. You would build them as an ultimate show-stopper. Especially because a Citadel has an anti-Titan weapon...
In addition, each new race will have a smaller deployable Outpost, which can be dropped pretty much anywhere where a ship can fly.
2. How does the galaxy described in your lore interact with the original Sins universe? (If we're allowed to know yet... I have the obvious guess ^^)
For background, if you haven't read it yet, you can read the Pangalactic War Timeline which describes the galaxy at large and the events which lead to the mod setting. Gameplay-wise, the link is mostly limited to lore and some of the visual design choices. For example, the structure I am working on now, the Capital Aperture, is designed to look like a sort of a huge "stargate" (only instead of shimmering surface you can actually see a portion of the Lost Hope, a giant citadel system from which Xin are staging their invasion) through which capital ships "materialize" instead of being "built".
3. Dynamic combat... I found out about this from watching your youtube video at least a dozen times... And while it's extremely aesthetically pleasing, I haven't grasped the tactical advantages of movement yet. it just seems like it would be an organizational pain.
In short, yes, working as intended. 
The idea behind DBS is to simulate, among other things, the chaos of battle. If you ever watched one of those documentaries about massive fighter plane dogfights in WWII, something like that. You've got fast moving ships all locked in a furball and, once the fighting starts, you better hope you came prepared.
The planning phase is limited to the pre-battle conditions. You can then pick your fleet composition, set your groups, arrange the initial formations etc. Once the battle starts, your micromanagement capacity, just like in a real "furball" scenario, goes down. There are ways to take advantage of that. Many of them depend on you being more prepared and organized beforehand than your opponent. If you have set up fire groups which you can direct from the overview, and your opponent hasn't, that's a major plus in your favor now. If you attack with a unified front, you can deal some good damage before the dogfighting begins. If you stagger your attacks so that the assault ships move in first, engage the anamy and then you move in your long range ships to focus-fire hard targets, you will have a much better result than if you tried to do all of that at the same time or just let them "do their thing". And so on.
Not all ships have dynamic movement. Long range ships and siege frigates typically don't move. You use them for busting capital ships, or structures - using them as a primary offensive weapon simply doesn't work anymore, even more so because they are weaker in shields and armor.
The ships that do move, do strafe. Which can produce all kind of interesting and even cinematic effects.
5. Will there be player portraits for Xin, Hegemony and Remnant forces, like how they have the spiffy TEC admirals' face you can pick from as your commander avatar?
Yerrs. Hope you like squid faces. 
Actually, I am also making a Xin portrait for the loading screen. So you guys can see the... nemesis.
6. Will there be voice acting for new factions' ships? Because that would be badass.
Yep. I am also implementing my "talents" in the field of sound mutilation so that a full range of (for the Xin) gurgles, squeals and intelligible grumbling can be heard from their ships as you order them to shoot hot plasma death at your enemies.
7. ETA yet? Estimated percentage of completion? =P
ETA - you know the answer, when it's done. 
I'm done with ship models, currently working on the structures and the various paraphenalia of the mod, such as icons, sounds, particle effects, research trees, abilities. Once the modelling is totally done I think release date will be announced as the coding doesn't take nearly as much time.
4. So, you're doing this alone? I can't think of a good way to word it, excepting Ryan Reynolds' quote from Harold and Kumar: "But why?"
Because I can? Nah, there are advantages to having a team working on a mod, and there are disadvantages. This way I have my own pacing, can implement my ideas and vision promptly and directly. The drawback is that I have cartloads of stuff to do myself, which is sometimes trying. But since I love doing it, I don't mind.
