Welcome to the community, E!
Your questions answered in order, then some comments on others' postings, and then some parting words.
1) What areas of the DMV should I avoid, and what areas are up and coming? Nothing I can provide here that @Russell Brazil would not be able to tell you in a 5 minute phone conversation. He's spot on and knows his stuff. I personally do not know the DC area as well because I focus just within the beltway and out from there. Everyone is spot on when they say you won't get cashflow in most of the Northern Virginia unless you buy the property outright.
2) Is this the best time to buy, or should we wait until interest rates come down bit?
I tend to side with David Greene here in that I practice my own advice. I just helped 3 clients buy investment homes in the last month and just closed on one in Annandale, Virginia myself. I believe the next 6-8 months is actually a prime time to buy, albeit a little risky. History states that as rates go up, so do mortgages. When buyers are priced out of the market, sellers get scared and the buyers left retain all the negotiating power. Between last year and this year alone it's been unreal. I bought in Springfield, VA last year at sub-3% rate and $25k over asking on a $625k house 2 days after listing. They had 72 showings that weekend and I was one of 18 offers. Now, in Annandale, just last week and 5 minutes north of Springfield, someone else sold me a similar $625k list house with $15k in closing costs and $615k final sale price. They had been on the market for 13 days with 1 offer that fell through due to rates rising and buyer getting cold feet. And I had all inspections/contingencies in place. Not floating my own boat here, but anyone who says now isn't a good time is A) misinformed B) not a good negotiator or C) hasn't been watching trends/human psychology long enough
> Where would I find a great buyer's agent?
Again with @Russell Brazil here, use the BP search tool or if you'd like, I can help you meet some stud friends of mine who match your goals and personality.
> Is it smart to buy some land near great amenities and build a new multi-family property?
Forget who mentioned it, but the only place you'll find land up by us is west on 66 in Centreville/Chantilly. Another option could be a buy/tear down/rebuild project. But you're talking at least $1.5m or so to do that right.
And that brings me to my closing comments. I won't insult your intelligence on getting your money right or knowing which books to read - sounds like you know exactly what you're doing and just need general rudder steer in a specific market. Recommend you consider Annandale (between Orange and Blue lines and near Inova Fairfax Hospital); Springfield (same reason); and anywhere in Fairfax County. As you head south on 95 you hit Woodbridge which can have good renters for MCB Quantico (which I know well). Going West on 66 might be your best bet for cashflow and equity growth combinations. They're usually $100-300k less than 10 miles East on 66 but have the same builds.
Best of luck to you and your wife in your endeavors and if you ever wanna shoot the **** or get set up on an MLS search non-committed, I'd be honored to help! Again, welcome to the BP fam.