With that being said, if you're comfortable with a long term hold, San Diego and especially coastal, will always be attractive imo. 

Whether you need a CPA with just three rentals depends on the complexity of your situation and your comfort level with DIY tax prep.If things are pretty straightforward, you might be fine with tax software for now.

Provided I can establish a solid investment plan tailored to their financial needs/comforts such as debt ratios and income, they would be more than happy to offer me some financial control.Additionally, If I wanted to, for the sake of building my own personal wealth, I admittedly have the luxury of taking a loan from my parents.

If you do not feel comfortable pursuing additional growth, I'd wait it out just a bit. 

Get out of your comfort zone.

Are there any challenges I might face, especially if my long-term tenants aren’t comfortable with the short-term rental activity in the same building?

Whether that's mobile home parks or any other kind of commercially valuated endeavor is a matter of personal comfort and preference.

There's a lot more compliance, regulations, and other protections that many brokers do not feel comfortable hiring just anyone. 

Get out of your comfort zone.

It’s better to have less rooms and to have them large enough to comfortably fit a queen bed.