You are absolutely right, you should be setting aside money for maintenance and unforeseen expenses.My biggest suggestion would be, if you really want to protect your assets, talk to a lawyer in your area about the best option for both you and your boyfriend. 

When they leave we will raise rents to total $3,900 or $4,000Monthly Insurance: $194Management fees: 10%Utility costs I will have to pay per month: $391Using the bigger pockets calculator, I'm not exactly sure what to include there for vacancy rate, repairs/maintenance, and cap ex.

If you can get a copy of the lease, review to see what the LL and Tenant responsibilities are for on-going maintenance.  

Here it is with conservative assumptions (opex 60% of gross income, incl vacancy, maintenance, etc.).The cap rate is 4.8%, the CCR is 1.1%, the CCR incl. tax benefit is 17.5%, and the IRR is 24.4%.

It depends on the reason for the loss.First of all, depreciation is added back to any losses.Secondly, if the loss is due to vacancy which has since been filled, that is taken into account.Thirdly, repairs and maintenance are generally added back in as well.Overall, debt to income is your overall monthly debt and housing payments (including HOA) to your GROSS income.  

It is a new unit and the vendor/owner seems very experienced.Repair vendor 2: Install a 3 ton 16 SEER LENNOX system, 10 yr wty (free maintenance checkup twice/yr).

(Make sure you do not go cheap and undersize your ac unit, you'll regret it later in maintenance calls or complaints of it not cooling the house off enough when it's triple digits and 75% humidity) If you need any wiring done, check out Bybee Electric - they'll get it done quickly and efficiently.  

I had a question regarding Annual Operating expenses (Operating expenses include: Taxes (property taxes), Insurance, Management, Maintenance, Utilities, and Repair.) 

Same old agent routine (because it seems to work I guess), tell the owner the inflated value "they want to hear", then start blaming the market and trying to reduce the asking price a couple of weeks after listing it.  

.- According to BP calculator, it should cash flow $1000/month using 10% for capex and 10% for maintenance.