My basement will have a private entrance and will be completely separate from the rest of my home, with a few locked doors in between me and my guests.I've been informed that I might not be able to use my current homeowners insurance policy. 

My husband mowed the grass twice while it was in our possession and I had someone put boards over the front door entrance as the glass door fell down after I bought the property.

Normally some kind of entrance fee...$20-$30.   

Turned a half bathroom in the private entrance basement into a full bath.

Separate entrances?

I own a 10 unit building which has 3 separate entrances/common areas with have mailboxes, stairwell, etc. 

Since this is an entrance to the unit, I would replace it.

They will have the front door entrance through the common space.

Assuming that you have to pay taxes, closing costs, realtor fees, etc, and you are left with 300K to invest, here's how I would invest it in the Denver market to achieve your goals:I would buy three large single family homes (6+ bedrooms, 3+ bathrooms) with basement apartments with separate entrances that cost between 400-450K with 20% downpayments in Westminster, Lakewood, Englewood, Thornton, or Northglenn, also, these houses would ideally be separated from the top and bottom (ex. 3 bedrooms 2 bathrooms upstairs, 3 bedrooms 1 bathroom downstairs), so you could rent by the room for a premium on the top rooms, and rent by the room on the bottom rooms or rent out the whole bottom unit to a family.

Hi there- Currently have an 11 bed student housing unit with 3 entrance doors and 11 separately keyed bedrooms.