Does the advice change if I say I most likely will retire and live out my days in the DC/NoVa area?
If you're planning on working and retiring in the same area, the area doesn't matter. Even in the rare case where it does matter, it probably doesn't make a difference in planning at this stage.
Does the advice change if I'm expecting to get married within the next 4 or 5 years? My boyfriend right now makes significantly less than I do (tomsang, I'm a woman) and I don't expect his earning potential to increase (by his choice, which I'm fine with) past 30k a year (its about half that now).
This is a good question! As a single woman making 56k, you're in the 25% tax bracket. As a married couple, you'd be in the 25% tax bracket if the two of you earn more than 75k a year. So no, this doesn't affect your decision.
This is a little off topic, but if your boyfriend makes 15k per year, he's eligible for the Retirement Savers Tax Credit if he contributes to a traditional or Roth IRA. This is a tax credit worth 50% of his contribution up to $2k if he makes under $17,250, and 10% if he makes $18750 to $28750. I've never been able to take advantage of this credit because I'm a student, but it's a great way for lower-income Mustachians to jumpstart their retirement savings.
I guess right now I know I'll go with a Vanguard Target Retirement fund but I'm still torn between the contribution tax options! Beltim, it's like you read my mind, I feel like I have to make The Right Decision or Else!
Since you're currently in the 25% tax bracket, expect to be for a while, and are unsure of your mustachian status, I would recommend starting off in the pre-tax (or traditional) 401(k) option. The 25% tax bracket goes up to $70k for a single person and $140k for a married couple, and it sounds like you think it's unlikely you'll make more than $140k as a couple, and from that I can infer that it's unlikely you'll need more than $140k per year in retirement.
If you're not convinced, or if anything is unclear, ask more questions. And remember, a suboptimal decision now is better than no decision!