It could just a joist issue which isn't an expensive fix or something to worry about.Check the ceiling for brown spots as sign of a current or prior leaking room.Window units in house means there is an HVAC issue no matter the reason given by the owner. 

I have 8 rental units now, with a goal to scale to 50 in the next two years.

My ultimate goal is to be involved with REI, but I am not sure where the best place would be to raise capital and learn.

If they do not have any then there is your answer  Just because a company can find you a good deal does not mean that they can get you the monthly return year after year on that property Always remember you own four walls and a roof ,they owned the business system it’s operating inside of that to give you the actual return that it was promised and that’s easier said than done if they don’t have correct policies procedures in structure Always make sure that your business model aligns with theirs to make sure that they are going to help you reach your ultimate goals well if they cannot have that conversation with you then maybe they were the wrong team to leverage your properties with

I typically send the video to the prospective tenant and have them fill out an application prior to a physical showing.

The financing becomes difficult, and I would have to acquire many, many individual properties to achieve my goals.

I have aimed to take achievable and actionable steps towards my goal of buying my first property with intention to rent or flip by connecting with local investors, evaluating deals, and of course listening to the BP Podcast/reading books. 

Having a real estate development company/ real estate holding company is the end goal but I just wanted input from all the pros out there on what would be best!!!

@Grant Dennis @Russell Brazil nailed it.In any negotiation, real estate related or not, it's critical to understand the interests and goals of each party.The seller's agent is required by law and by ethics to get the best possible deal for the seller. 

I’ve included a link below for a table showing the population for cities in Polk County, categorized by a person’s place of residence in the prior year and their citizenship status.