Hey, Neil. My fiancé and I went through a similar search process recently when looking for a house in the DMV to house hack. In my experience, rents are higher in DC and its a bit easier to find/convert a basement into an in-law suite (since you want to avoid sharing space with potential roommates). $800k can get you some decent row house in DC where you can easily create an English basement that would be great for AirBnB or a long-term tenant. Some neighborhoods that come to mind are Brightwood, Takoma, Manor Park, and even parts of Fort Totten, Brookland, and Michigan Park. All of those neighborhoods are relatively metro and public transit accessible and can attract great renters.
However, if you're set on staying in VA the two key questions are what is your potential exit strategy and how much effort do you want to put into that? To address all your options above:
1. I think this is the best option, since Del Ray/Old Town is an excellent location and attracts good tenants. If you're not looking to share space with roommates, its definitely still a win that you can lower your housing expense while building equity in an excellent neighborhood. However, I don't think a ton of properties in those neighborhoods would rent for $4k+ a month if you were to move out. So your exit strategies are to rent by room after you move out (higher effort than traditional whole house rental) or to sell the house, but that might mean you need to stay there for several years to ensure you can make money on the sale or do improvement (potentially medium or high effort).
2/3: Huntington and Falls Church are also solid options and a SFH is definitely attainable. I think that strategy is okay and might open you up to being able to rent the whole house after moving out, since price points are a bit lower. Renting out the entire dwelling is definitely lower effort than rent by the room, but you are correct that rents are typically lower in those neighborhoods, especially when not close to a metro. The WFH/Uber trends might be changing that, but metro access and DC proximity are still selling points for now.
4. I am personally not a fan of condos since it seems like you'd have to put a decent amount down for them to cash flow. And you have to deal with HOAs which can be hit or miss. But they are typically in prime locations and might be less headache, so if you're choosing to keep it as a rental after you move, thats a plus.
The DMV is a tough market for sure right now, but you definitely got this and can figure something out. Best of luck with your search!