Did you work with any real estate professionals (agents, lenders, etc.) that you'd recommend to others?

Quote from @David Strunk: I know this question is off topic but I am also in NC the Charlotte area and was wondering if you could recommend a good CPA?

I also highly recommend being represented as a buyer. 

Feel free to reach out for some recommendations. 

(ii) Can anyone recommend an agent in the Philadelphia area who specializes in apartment buildings? 

I highly recommend hiring an attorney, at least for your first time.Some attorneys specialize in evictions.

have a rental (multi family 2-4 units) needing major rehab. interested in learning what work can be learned/performed easily and what needs to be hired out to a contractor. recommendations for learning resources for DIY rehab (good youtube channels, etc) would greatly appreciated!

For lenders, I have access to private money lenders or if you want to go the traditional route, I recommend checking out Coast to Coast - Jeff Weller. 

Would you recommend the route of a first lien HELOC based on the above situation and information?

Some will follow staff recommendations almost all the time .. others will not..