Answering in no particular order:
I think Garrus and Shepard will go out in a firey blaze of sniping action together (at least, that's what I want) but I don't think they'll necessarily be either vigilantes or officers. I feel like they will pretty much go whereever the wind takes them (so a little from column a, a little from column

. At least, this is what I'd like to see. If BW decide to force a 'Shepard sacrifices him/herself for the greater good' endin on us, then I actually think I want Garrus to go out fighting along side. Not that I want Garrus to die: I just think that's where he belongs.
Garrus needs more Grunt banter. And Mordin banter. Grunt, because his krogan banter is always gold (the brief back and forth they have on Mordin's recruitment is amazing), and Mordin because he's so unlike Garrus, it makes me laugh to think of it.
I think the reaction would be mixed. Some crew (Mordin, Grunt) would probably not really care about the species thing, but be happy for Shepard. Some (Jacob) would take issue with it out of jelousy (I know he is Mr Nice Guy, but he is also Mr Sore Loser). Kasumi would be thrilled for them. I think Miranda and Jack would disapprove. Samara, I think, would be happy for Shepard. Zaeed... well, I think the idea would turn his stomach and he would say so. Legion is legion. Tali... I'm not entirly convinced Tali wouldn't be a tad jelous as well, one way or another. lol
Garrus looks good in blue.
I don't think Garrus and Shepard need to say the 'L' word. They aren't really the 'talk these feelings out' type of couple, and I think the emotional sie of their romance is already conveyed so much in body language and Shepard actually stopping him from speaking, that when they get to that point, they'll both let the other know without actually needing to say it. I think saying it would go down the dorky/cheesy road again, and it doesn't need that.
Garrus is one hell of a sniper. Scoped and dropped!
I don't think the romances should be part of the overall arc of the whole trilogy (eg, your relationship is KEY to saving the day), but they definetly need to have some significance on the ending. Whether that be that depending upon sucess, Shepard lives out her life with her LI (differently for each, in character fitting fashion); said relationship influences a descision which affects the final fight; or simply that's the person Shepard has at her back in the endgame - make more of it, please. If we simply get a 'one night before dying' scenario again, I will be disappoint. Please let the relationship be a proper relationship and develop as such throughout the game...
I definatly want conversation options which relfect the specific routes I've taken with my relationships (actually, wth ALL realtionships. Not just LIs. Yes, I am greedy). If Garrus and Shepard have history from ME1 - mention it. If they hooked up in ME2 without said history, show the difference, howver small.I don't care if I need to replay to get all the conversations with him (eg, a bromanced Garrus should have bromanceable dialogue as well). I love replaying, Let me have a new experience.
Garrus and Kaiden: Garrus would defend Shepards honor, and Kaiden would be in disbelief that she chose Garrus, but noether would come to blows over it. They both respect Shepard too much and are too in control of their selves and the mission to do anything other than abide by her descision. However, the 'loser' will certainly warn 'the winner' : "If you hurt her, I'll kill you."
Garrus and Liara: hard to say. Garrus might be quite dignified about the whole thing, but Liara seems like she could snap and go mad at Garrus for 'stealing' Shepard from her. To which Garrus would probably reply that Shepard makes her own choices and they both know that. Also, that Liara has changed. Liara may want to bring her part in Shep's resserection into play. Who knows?
I'm hopinh ME3 will start pretty soon after ME2. Long enough for the Reapers to make their next move, and for everyone to deal with the fall out of ME2, but not so long that we have the team drift apart again. Ideally, we'd get an expansion pack to bridge the time-gap between ME2and ME3. I want continuity, dammit! No 'clean slate' beginning again.
FemShep's power level is almost certainly over 9000. According to the scouter, anyway.
BW employees would need a damn good fortified base, that's all I'm saying. But without Garrus V to help them... not long.
And... hope this doesn't get stuck in bandwidth. lol