I don't doubt that you've considered all these factors, but here's a list.
1. Taxes: Multifamily had a huge jump in Harris county this year, and it sounds like a lot of other counties have done similar. If the 2019 assessment isn't out, I would estimate on the high end.
2. Get thorough inspections and leave no stone unturned. Be aware of the age and condition of water heater, HVAC, roof, electrical systems, plumbing, etc. Any of these having problems in the first couple of years can turn your numbers upside down if unplanned for. I would set aside some cash flow every year for capital expenditures.
3. Is there an HOA?
4. Is it in a MUD?
5. Is it in a flood zone? Have you received an insurance quote?
6. I would plan for 10-12% vacancy every year unless you have some sort of confirmation from the market that it is lower.
7. If managing yourself, It's not much, but set aside $25-50 bucks from cash flow every month for advertising. When it comes time to lease, this can be a good nest egg to put toward marketing your home.
8. If having it professionally managed, build in 8-12% for management and make sure you have a detailed breakdown from them on the additional things they would come to you for.
9. Make sure you are researching your comps in the neighborhood every 6 months so you have your pulse on the market, how long homes are sitting unleased, and what rental rates are at.
Good luck!