Even if you're planning to do 100% of the work yourself (And I hope you're not), materials alone will blow your budget by a lot.Just looking at the pictures you've put up, I'm willing to bet there's some DIY electrical.

You gotta know electrical, clear span, loading docks, ceiling height etc...

I see he converted it to gas heat, but I think in my experience that new windows, and installing electric baseboard heat which the tenants pay is the way to go.

Mold, bad plumbing, bad electrical, structural damage can all be high risk items. 

I have a 4 unit house and the electric company took the meter off for one of the apartments.

You say your doing a Full rehab ( walls, electric, plumbing,etc).  

Your most expensive areas will most likely be ADA/Handicap access, Fire safety/prevention, and electrical (is this aluminum wiring and are the panels Federal Pacific?).  

I switch out all the electrical sockets and light switches from the pole type to the one piece with unbreakable strike plates also in white.

I got this great house that needs some changes, such as replacing windows, new electrical, some plumbing and turn down a kitchen wall to create an open concept living room.Well, I got advise to hire an architect to create the drawings of the house.

Different roofs, A/C systems, furnaces, water heaters, electrical, roofs, eviction processes can vary, likely the same management company does not cover the whole area you will buy the houses in, etc.