I am not sure where to begin. with your septic and well you'll need to do site layout first with a land planner or the county. after that you'll need to check setback requirements and design plans and start budgeting with a builder. once you have a confirmed plan set and budget broken down and builder selected then you can talk to banks. most people think it starts with banks 

While I do like new build for new investors because you get a builder's warranty, better insurance, and first take of renters, you may have to overpay right now which could hamper the scale of your investment.

Finishes builder grade or a bit higher such as luxury laminate, run of the mill kitchen shakers. 

People use it because the higher LTVs allow them to raise less money (which newer syndicators and “portfolio builders” need), and project higher returns (which attracts capital from investors who might not fully appreciate the risks).  

Seeking recommendations for a duplex or fourplex builder in the Phoenix area and the construction cost per square foot.Four years ago rough estimates were at $100 sqft, now I'm seeing about $200 sqft with another $50K for site preparation. 

While this isn't a long-term solution, it could buy you time to arrange finances for a complete fix.Insurance Claim: If the issue with the tub is due to improper installation, it's worth checking if this is something that your homeowner’s insurance or a builder's warranty (if still valid) might cover.Partial Renovation: Instead of a full demolition and remodel, consider if there's a way to repair the tub area without a complete overhaul.

I think it is best we work together to find an experienced developer/builder, do you think so?

New homes for $250K where builders are buying rates down below 5%.

Acquiring land seems to be the biggest hurdle for many spec home builders.

Find a builder, a GC and He would take it from there.