Let's say my 1st mortgage balance is $600k and I want to take out a 2nd mortgage for $150k for home improvements which makes the interest on the 2nd deductible as well.

The buyer must come up with the difference between the seller(s) current mortgage balance and agreed upon sales price, plus closings costs. 

Link below.Per the forum post, you only have to pay interest if you collect a greater security deposit than one month’s rent, and then only on the balance that is greater.

Here’s a detailed breakdown of these two types of markets and the factors that contribute to each:Cash Flow Market, a cash flow market is one where rental income exceeds the expenses of owning the property (mortgage, taxes, insurance, maintenance, and property management), resulting in positive monthly cash flow for the investor.Key Characteristics:High Rental Yields: Properties typically have high rental yields compared to their purchase prices.Stable or Slow Appreciation: Property values increase slowly over time, if at all.Lower Property Prices: Generally, property prices are lower, making it easier to achieve positive cash flow.Higher Rental Demand: Strong demand for rentals due to economic factors, demographics, or local employment conditions.Factors Contributing to Cash Flow Markets:Economic Stability: Stable job markets and steady local economies that support rental demand.Rental Market: High percentage of renters compared to homeowners.Affordability: Affordable property prices relative to rental income.Local Policies: Landlord-friendly laws and regulations.Appreciation Market, an appreciation market is one where property values increase significantly over time, offering substantial capital gains upon sale, but rental yields may be lower, resulting in lower monthly cash flow.Key Characteristics:High Property Value Growth: Significant annual increases in property values.Lower Rental Yields: Rental income may not cover the monthly expenses, leading to lower or even negative cash flow.Higher Property Prices: Generally higher property prices, which can make it harder to achieve positive cash flow.Strong Economic Growth: Rapid economic growth, population influx, and development.Factors Contributing to Appreciation Markets:Economic Boom: Strong local economy with job growth and high-paying industries.Population Growth: Influx of people moving to the area, increasing demand for housing.Infrastructure Development: Significant investments in infrastructure, amenities, and services.Desirability: High quality of life, good schools, and attractive neighborhoods.I hope this information finds you well. 

It's all a balancing act of course, but it all comes down to finding the right market that matches your goals and working with the right team. 

STR can be more profitable if you set it up right with your pricing and have a balance of making your place look nice, while not spending too much on your setup.

Can you please share more of what you're looking to achieve?

Not sure whether there is currently a lien/balance on the condo, so I'm just spitballing - this may or may not work for you. 

Otherwise you are looking at mid to high 7s at par If this is an investment property, you can achieve a rate in the high 6s on a DSCR based loan with a low LTV, high fico, high prepayment penalty period. 

I would like to have a good balance of positive cash flow as well as appreciation.