Are you planning on renting out all four units or living in one?  

We had units in San Diego at the GR.  

Recent updates include luxurious vinyl plank flooring throughout, fresh interior paint, new lighting fixtures, and solar panels.

I am very new to REI and would like to know if this is a great opportunity to buy in an up and coming area or if the residential properties will negatively impact my ability to rent out my other unit.

There was a fire escape staircase for the upstairs unit that was made with wood( not metal that was about to fall apart.

Multi-unit and MTR/STR (where allowed) can help counter that, but otherwise it's quite speculative.

Think of it this way - you have two communities with 1 bed 1 bath 900 sf units.One has a HOA fee of $350 and another identical is $650 - which units will have higher valuations? 

The current seller has done a complete rehab on the property and is now selling it vacant.My question is: Am I allowed to rent out the units at market value given that the property was previously under rent control?

I moved from Pensacola, FL to Columbus, OH to start investing in 1-4 unit LTRs.  

You could also tell your tenant to just get a standing unit that doesn't need to be installed into the window itself... or just shell out some $ for a split unit :)