Quote from @Sami Gren: I start by making the original tenant fill out a form requesting to add a new renter, and they pay me a $50 processing fee (I charge a $50 fee any time I make changes to an existing lease). 

These programs often assert to guide you step-by-step through the process, provide assistance with funding, and connect you with contractors.

I wanted to offer him about $50K over what is remaining on the mortgage and go through the 60-90 day process to assume the existing mortgage.

In a city like Philly, you will face many challenges - you need to learn the market and know the neighborhood and the block and make sure all of your numbers are within reason, you need very reliable contractors, you need a to understand the permit process, you need to be familiar with market expectations. 

It's the simplest way and walks them through the entire STR process.

Make sure it explicitly explains the process for termination if you are unhappy with their services, especially if they violate the terms of your agreement.3.

Starting with a smaller property or a few fix-and-flip projects can help you build equity, gain credibility with lenders, and better understand the process before scaling up.Securing funding for larger projects can be challenging without prior experience, but options like hard money loans might be worth exploring.

Its relatively easy to manage the process once you do it a couple times.   

I had the most streamlined process, and it was truly a DSCR loan.

I would explain to them your process of handling requests, response times, property inspections, and so on.