Kristin, your diligence is admirable.
For the multi-unit, I would also gather other agents opinions in the area to see if the overall thesis on the area is a negative one. In my opinion, that might be a sweet niche of house-hacking a fourplex in a military town and have all of your tenants also be servicemen and women. ( I would have your husband see what the general consensus is on base before doing this). For the flip, I wouldn't go off of Zillow to determine the ARV's, I would just have a local agent print up comps of everything within a half-mile radius.
If you ultimately want multis in that area, and their aren’t any on the market, it’s going to take some HUSTLE. Whether you do driving for dollars then skip trace the owners. I know @Cornelius Garland has a fantastic and very affordable skiptracing service. Or go directly to the tax assessors office and have them filter out a list of multis in the area, then skiptrace the owners personal information to cold call or direct mail.
It ultimately is going to come down to what your risk tolerance is and how much time you have to put in the work required. Hope this helps !