@Jonah Slove
Maybe you, Jonah, should get a prenup to protect yourself. Now that everyone should have a prenup and you'll get divorced scenario is out of the way so she/you should cover yourself is covered I'll answer as if this was me in her shoes.
If marriage is near I'd wait and consider selling to get the $500k tax free, so long as you qualify. The exchange is great but just kicks the tax can down the road. Tax free money all day long, you're now playing with house money. I would not invest in Detroit unless you are from Detroit and know the area very well. I would and do stay close to home in a decent sized city so you know and are familiar with your rental market. I'd get a few smaller sized properties 4 units or less so the property is more liquid, next thing you know you find out in a few years that this isn't your game and you want to change your investment strategy and if it's your game it'll be easier to cash out/trade up. In addition I'm guessing you're both W-2 employees, financing 4 units below will be a little easier.
Don't scale too quickly, you're not going to miss the boat. Looking back a year and a half ago, people would now say you shouldn't have bought then. I bought a few properties then, bought them right and still sold for a profit within the last few months even with the interest rates tripling. The best time to invest is always today, just buy right, don't pay market or over. You don't want to be in a position of I have to get this one, wait for or structure the right deal to make it good for you. Negotiate the right deal and you'll always be good.
Buy and hold, you will most likely look like a genius in the next 20 years. As the late Will Rogers once said "Don’t wait to buy real estate. Buy real estate and wait." Enjoy the journey man and definitely enjoy the time with your fiancé and soon to be wife. Real estate is the best way to create a life to enjoy the most precious asset we all have, time. Life is too short to worry about all the small stuff and nonsense the internet creates for us. Good book recommendations if you haven't read them; Medici Effect, 4 hour work week, F*ck your feelings.