It is a matter of personal choice to use the HELOC.  

I don't think that's the 1st choice of any developer. 

The classic example of legit "unforeseen" is that your mom who lives 3 states away comes down with terminal brain cancer and you want to be near her for her final months.

I think that if you have a choice of making it into a third bedroom and private bathroom with its own entrance.

Then add the value of the park owned homes/stick-built house separately to your final purchase price.

There is no one way and it depends also on how you choose to operate your business.Monthly rent...dependant on property, market drivenUtilities....specific to property and marketsinternet, cable....market drivenTenant or landlord costs.. market and landlord choice

Your other question is a little more involved but I will say that I looked a several properties in the Truckee/Tahoe Donner area before finally buying one in Tahoe City earlier this year.   

Hey BP team,My name is James Derrick and I am finally serious about beginning this real estate journey.

The best choice we made was performing full inspections, and asking the owners to fix the items discovered.

The final thing to consider is tax treatment.