@Gabriel Krut - first off, good for you for getting started investing in real estate early in life.
I actually also live in SD and invest in Grand Rapids, and have few thoughts on your analysis:
In GR, landlords typically pay for water. This will cost you about $50 - $75/ month and should be included in your analysis unless you think you can get $1,800 in rents while having the tenant pay for water.
Also, landlords typically pay for landscaping and snow removal in GR. That will run you about $100/month and should be included in your analysis.
You've got management fees of 10%, but will your manager also take a commission for signing a new lease? Many managers do (it can be 50% of first month's rent), and I would include that in your cash flow analysis too if your manager will charge that.
Is electric split so that each tenant pays their electric bill directly, or does the landlord have to pay for electric?
Are these units currently leased? If not, how much will you have to spend to get the units rent ready?