I was planning to start with a duplex, tri or quad but if buying an apartment complex is possible.

Or if you have a few residential properties and one large apartment complex, I'd have the complex in its own entity and the regular residentials in the 2nd LLC.I don't know how much it costs yearly to have a LLC in your state, but think of that.

6 plexes are considered multi-family so you can assume that the owner of the complex is an investor as well.

I found a seasoned mentor that is a Property Manager of an apartment complex and have her own PM business.

I am overseeing the turnaround of a large apartment complex, 100+ units, where most of the units are vacant and in need of serious rehab.  

Isn't this part of the reason a lot investors like apartment complexes... minimizes risks?

I have over 30-40 homes/apartment complexes I purchased under $30K and placed Section 8 tenants in them.

Number two to market a rental in a condominium complex, if it's hard to get inside the complex a lot of times gives the person that is looking for the property a hard time to find it.We've had a lot of problems with condos because agents and other people cannot find the unit and cannot get inside the unit and some of these HOA's do not allow you to put for rent signs outside of the complex which reduces your ability greatlyAlso you have  no control on the HOA fees.

I am relatively new to real estate investing, and I am looking to invest in single and multi-family properties (and one day apartment complexes).  

If/when I have $1M, I would look at investing it into value-add or income producing multi-family apartment complexes or retail strip centers.