In other words, how would I calculate the return (from a purely financial standpoint) of "investing" in a primary residence vs renting and putting the money elsewhere (perhaps even into an investment property, but also considering buying a business)? 

Is it not problem that they do not have enough water. 

This is typically more favorable than financing for purely investment properties.Income Generation: You can rent out the other half of the duplex.

Roll it into the rent with a lease clause that anything over $X is split 50/50 between both tenants and you don't care who uses more water...In short, spend some money and make it a legal duplex or at least make it two separate units.

They're designed for owner occupants but could be something in which you occupied for a duration of time and then converted to a pure investment later. 

Upgrades/repairs include:flooring (tile and carpet, entire house), painting (entire house), complete kitchen renovation with new appliances, cabinets, sink, lightingcomplete bathroom renovationsupgrade/replace ACupgrade/replace existing hot tub  upgrade/replace furniture/bedsupgrade/replace old pier with newadd new kayaks, paddle boards, and bikesI am thinking anything that is removable (furniture, appliances, water toys, bikes, pier, etc) could qualify as an asset for the LLC and thus be used as a tax expense for the LLC.  

Food, water, shelter, the fundamental human needs.

> Military husband/wife buy new home, divorce, stop paying note and hoa> Husband is erroneously removed from title by tax appraiser, HOA forecloses on wife, I buy home at auction> Now I am on title, wife and husband on note, bank cannot foreclose because husband is protected by SCRA > (more on this in the above post, but husband does not want the house back)A while after moving in I discovered water damage inside a wall where rain has been getting in due to needing a new roof. 

How do I handle the water being in my name as well?

We are in uncharted waters.