It had an air conditioner, water and electric.

I probably will need a contractor if the repairs are serious (ex: roof, plumbing, electrical). 

 Also i was wondering of anyone here in the forum has installed solar panes to their apartments and how do you manage thr electricity bill with the tenants.

From your list, its clear you will need Mechanical and Electrical engineers.

We were not impressed until we came across a contract sitting on the swollen formica kitchen countertop that the former owners signed which basically read that whoever became the new owner would inherit $67k dollars worth of free renovations.We got impact and sound insulated windows and doors, a NEW AC unit and AC ducts, insulation in the attic, they increased the amps to the electrical.

Fortunately, electrical, furnaces, and water heaters had been upgraded.

I also learned to get the details on the water/electrical before putting the new tenant in and put a clause in the contract that they have to get it switched over or else there will be fees.

Found out that the HVAC condensation tube was running to the outside gutter drain (previous owner did this) and unsure why this didn’t show on my inspection report... so, the pipe froze and backed up moisture causing the electric pilot to burnout.

Variable expenses like water or electricity can come back to bite you. 

No matter if you do 20 or 30 year, I bet you can do better than 4.5%.What about house electric, like hallway lights?