If you need to obtain it, how difficult will that process be?  

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). 

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 forever destroyed by the process of securitization.

I’m in the process of getting my real estate salesperson license to gain access to MLS listings as well.

Work out a fair revenue-sharing model, such as a flat lease or percentage of profits, and consider hiring a property manager for oversight.This post does not create a CPA-Client relationship.

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.

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

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.

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