I think you've got this site confused with Mission Impossible. I read your "question" and I hear, "Your mission should you accept to choose it...."
Honestly your question is about a dozen questions that each lead to several questions requiring answers from you. No one reading this is going to be able to "answer it." If you're interested in getting some assistance with investing in the Arlington VA / Washington DC area, my suggestion is to click on the find an agent tab in the green bar on the top of every Trulia page, and look for a few Realtors who work in that area and who have experience with investors and good ratings/reviews. Then be prepared to sit down with them and have a conversation. As someone who has worked with many investors I can assure you there are as many investment strategies as there are investors. You need to be able to tell the Realtor what your objective is, flipping isn't the same as buy and hold and the criteria for analyzing various properties changes with the investors objective. Most serious investors already have their own metrics for calculating ROI and investment potential. Reading your question, I suspect that you're new to real estate investing and what you want is some guidance, which is perfectly fine but in my opinion you'll do better having a face to face or telephone conversation with an experienced Broker in the area rather than using an online forum. Best of luck to you.