I think it's 4 or 6+ units, so it depends on what you are buying.

Depending on town regulations, most all have it outlined in their contract verbiage that the septic tank is to by pumped, collapsed and buried.This was truthfully a small expense in the grand scheme.

Changing your policy mid term isn't always difficult just depends on the Carrier's cancellation policy.  

Like mentioned it can depend on goals a lot.

However, if it's still the best deal around, and doesn't need any work, and you can find great financing, and and and....Also, it depends on the cost of utilities in your area.  

In regards to question #2, really depends on your credit, experience, income and liquidity.

Depends on how big of an area and how serious the issue is.

It all depends on the tenants staying or going and what costs I need to outlay to acquire new ones.  

It depends on the individual investor.

Just a preference and I don't think it would be difficult to upkeep, but that depends on the tenants and if they charge extra to mow and trim.