Brittany, welcome (early) to Atlanta! First, let me say I love the idea of a duplex BRRRR or buying a multi-unit property. In general, I say buy a good investment deal when the opportunity presents itself. Bonus if you can live in it, too!
I'm a broker and Atlanta native. I grew up in Alpharetta and currently live and work in Alpharetta but have lived in Grant Park and East Atlanta (both are next to Cabbagetown), Decatur, Brookhaven, Dunwoody, Cumming, Roswell...and...my mother lives in Martin's Landing! I have advice on how to select the right part of town and pick the right home; however, buying a home is a very individual decision and it is a "major decision".
Before personally diving into real estate, I heard some old wisdom suggest not buying a home within 6 months or a year of another major life event (marriage, new job, new city, new baby, etc.). This idea may be challenged by the "real estate machine", but you have several overlapping major life events. No harm renting here for a short time while you get your bearings in a new city. That said, we bought our home immediately after having our first child and we're doing just fine. If I had to move across country to an unfamiliar city, I'd sell/purge almost everything I own to simplify the move and I'd strongly consider renting. There are a lot of apartments and short-term rentals geared toward longer stays like corporate rentals (furnished) and AirBnB rentals (furnished) are becoming more prevalent. Properties (rentals and purchases) are flying off the shelf. With fewer strings attached, you'll have boots on the ground and be able to learn geography, logistics, and neighborhood attributes, plug into the community, and meet a great agent.
My ATL-specific advice is to consider how the following factors fit with your current and future personal/family situation and your investing strategy/goals: Costs and challenges of the cross-country move; how long you plan to own a property; self-managing vs. paying for property management; expected time in new job(s); income trajectory; commute time/traffic; school system quality; childcare (cost, availability, logistics of childcare); and expected work schedule, etc. If a BRRRR duplex works with your investement strategy and meets your near-term personal housing needs, there's a lot of flexibility on the rest of the factors above...
...Except for TRAFFIC! ATL traffic is terrible. Since work will be in Alpharetta, I'll assume that area is at least partially important. The quality of life in Alpharetta, Milton, Roswell, and Cumming is exceptional. Getting aroundwithin those areas during traffic is manageable, but getting to/from them during Rush Hour is a beast and our public transportation system isn't great, yet. Also, Alpharetta and a lot of the other northern suburbs have fewer multi-family opportunities and generally higher price points for SFR. If duplex and 300-400k are concrete criteria, there's a reasonable chance you'll wind up commuting from another part of town. This may be completely fine before you have kids. As the family grows, the expectations and priorities driven by your personal situation may change a ton. For those reasons, include property management fees when you analyze your BRRRR duplex...you may end up moving to another area of ATL and not want to self-manage.
In general the northern burbs have great schools, more childcare options, and larger lots with bigger yards than you'd typically find in the "intown" neighborhoods like Cabbagetown...that's a huge generalization. Some intown pockets, like Decatur, have pretty good schools, too. Private schools are options, too. You may want to search for properties in communities near major arteries like GA400/US19, I-75, and I-85 come together, too. Older downtown neighborhoods like Cabbagetown, Grant Park, Inman Park, Old Fourth Ward, Kirkwood, Reynoldstown, and adjacent areas have a lot of neat older homes and some smaller multi-family properties. I didn't encounter many traffic issues getting around those neighborhoods on surface streets. You can still expect traffic on those main highways but at least those neighborhoods are pretty close to the highway.
Send me a message if you want to connect to kick around some specifics.