If only half the rent is paid, they are still 100% responsible for being late and subject to fees or eviction.Personally, I wouldn't want a married couple renting a room because that will result in an increase of utility use, wear-and-tear, etc.

The only other change will be repairs/utilities and they will be affected by inflation.

Each unit self sustained. 

Side Question:I don't want to complicate my primary question with any more variables, but as a secondary, ceteris paribus question.... if the owner lives part time in the STR how does one write off expenses not directly related to STR operation, such as insurance and utilities? 

They have better collateral and you are able to utilize your funds for renovations instead of the down payment.

Should I reduce the offer price and not collect monthly rent but ask that they pay utilities and other stuff like cable, etc?  

Or if the site needs to be rezoned- locations of existing utilities. - Stormwater/detention requirements and any restrictions due to site topographyFrom there you can go down the road for a surveyor and a full engineering contract. 

It is a fourplex with a SFH on the same property, on market (98 days), where tenants pay all utilities.

In case you are eligible for the Solo 401k, here are some of the benefits it would offer compared to a self-directed IRA:Solo 401k contributions limits are roughly ten times higher than IRA limitsThere is no custodial requirement for the 401kYou don't need the additional expense and administration of an LLC to have checkbook controlThere is a built in-Roth component whereas IRAs are either traditional or Roth, not bothA spouse can also participate in the same Solo 401k planThe Solo 401k has additional tax benefits over an IRA when investing into real estate using leverageThe penalties for prohibited transactions are less severe, though it's best not to utilize this benefit :)

Is that market sustaining rental income?