Hi Sebastian!
A few people have responded about the PMI and I absolutely would agree with them. As a househack and starting your real estate journey, ask yourself if you are seeking cashflow or appreciation. If your main goal is to decrease your monthly expenses, then if you have the extra money to buy it out that would be the best way to do so. If you don't mind paying more each month, you could put that money elsewhere and maybe make more from it! I would say it is important to consider the opportunity cost of your choices and look over your goals.
With respect to the downpayment, I think again weighing your goals is important. The best bet is to probably discuss this with a loan officer who (hopefully) can give you more information about the exact costs. I'm not sure what your local market (Reston, Sterling, Herndon) is like, but certain markets are in a position where they may see housing prices decrease in the coming months. Putting 10% down may give you more of a cushion against this and again (if your goal is cashflow) you would have a lower payment all around with your PITI and PMI. On the otherhand, putting 5% down frees up more of your capital for other investments (perhaps adding the ADU) which would generate more income in the long run.
So no straightforward answer, but I would strongly reflect on your goals and your willingness to accept risk and decide with those in mind!