From there you can develop a strategy with mostly cash flow that can help pay down your loans or invest in an appreciation market and buy and hold for a few years and pay down your student loans on the sale. 

He is willing to pay six months in advance.

How to increase the rent for this property with the section 8, and is that affect the tenant's portion of rent he is paying?

Many lenders also offer an Interest-Only HELOC, with which you pay interest only — no principal — during the draw period (Usually 10 years).

we had that property under 2 years and we pay a lot of mortgage. 

But as the previous owners didn’t pay their mortgage how likely are they to pay the rent? 

Borrow the money from a relative and pay them interest.

The roofs were updated in 2021.All units are currently occupied on month-to-month leases, with three tenants paying $1,425 per month and one tenant paying $1,300 for handling lawn care and maintenance.

Note: the $1423 amount includes owner paying for electric, gas & water.

Major remodels generally don't pay back in value unless the comps in the area have certain features.