If the cash flow on the existing properties goes close to breakeven, seems like you would be increasing your risk of large capital expenditures, like roofs or heat pumps, without cash flow to sustain them. 

Evaluate operating expenses, including property taxes, insurance, utilities, maintenance, property management fees, vacancies, and capital expenditures (CapEx), to ensure accurate estimates.

There's a pretty good chance you gave them permission to hire whomever they wanted and charge accordingly unless you have a dollar limit on expenditures. 

To maintain profitability, it's essential to carry out in-depth market research, closely monitor remodeling expenditures, and do due diligence on prospective properties.Preliminary Advice for First-Time Investors:Become knowledgeable: By reading books, listening to podcasts, using internet tools, and connecting with seasoned investors, you may keep up your real estate investment education.Start modest: Start small and increase your investments gradually as you acquire confidence and expertise.Network: Make connections with other investors, real estate experts, and mentors who can offer advice, encouragement, and insightful perspectives.Make a good plan: Make a thorough investment strategy with precise objectives, deadlines, and exit tactics.

She also issued a multi-page memo when form 3115 (repairs vs capital expenditures) came into effect explaining the ramifications to real estate investors, and whether and how they should file the form (All this was included because you were her client, and she files the form for you.) 

Major expenses that are often overlooked are capital expenditure repairs, roofs, hot water heaters, HVAC etc. 

He discusses capital expenditures, turnkey properties, cashflow, and why he thinks that $40,000 properties won't cashflow.

What is my reservesamount that I need in case of unexpected capital expenditures?

The rent needs to cover the mortgage, vacancy, insurance, property taxes, repairs, maintenance, property management, capital expenditures, and any other expenses that are applicable (utilities, snow removal, landscaping).

How can these cost-estimation principles be leveraged to create a more robust financial model for long-term rental property investments, considering factors like ongoing maintenance, capital expenditures, and market fluctuations over time?