First, congratulations!
Second, you're in MO, so I sincerely doubt you're going to experience a true "bubble" in the market. People "lose everything", when the market crashes - usually - do to financing. Here's the deal...
If you finance the property in a sensible manner and with a fixed interest rate, it doesn't matter what the market does, as long as you can keep renters in it. As long as your rental income at least covers the financing and cost of ownership, you're golden. You may not be making money, but you're not losing it either. Now, if the property values drop far enough, you may not be able to sell the property without taking a loss. However, if it isn't costing you anything, why would you HAVE to sell? Generally, you would only be forced to sell, if you had gotten into financial trouble in another area and needed to get your equity out of the property as a life raft.
I don't know what your market is like or what your financial situation is like. However, unless you are sitting on a ton of capital, I would use flipping to fund your long-term hold acquisitions. Personally, I would see if I could do a couple more great flips. Then I would set aside enough of the profits to provide a down payment on my next flip and fund the rehab. That way I'm not paying high hard dollar rates. I would use the rest to put a down payment on my first long-term hold acquisition. Then just lather, rinse and repeat. Get yourself enough SFH holding and use them to leverage up to multifamily.
Don't look at it as either/or. Figure out what your goals are and then leverage the different strategies to reach them.