Depending on the type of loan, you may not get to 75% because the cash flow will not be sufficient to support a 75% loan. 

Would that be sufficient?

Is this an FHA self sufficiency issue.

However if you plan on buying 3-4units, there is a trigger rule for FHA, it is called the self sufficiency test.

Filling the tank yourself with sand or gravel and saying it is abandoned is not sufficient to meet remediation requirements.

I would focus on quality flips over quantity.

But, it's very very likely you'll have to deal with one or multiple of:Drainage issues that have caused undiscovered damageAge and material of sewer lines and water supplySettlement or expansive soils causing problemsCentral systems (not having sufficient or central heating / ACJust some examples. 

Make sure the building you buy has sufficient parking for 6 units.

Your basic insurance policy with $300,000 in liability coverage should be sufficient in 99.999% of all lawsuits.5.

Your basic insurance policy with $300,000 in liability coverage should be sufficient in 99.999% of all lawsuits.5.