I would select a market which has strong rental demand and affordable entry costs like TX, then I would calculate basic deal metrics which include cash on cash return and monthly cash flow before I start my advanced analysis.

First, basic accessibility is not sufficient on its own to exceed unit numbers in RT-3.5 zoning and an ADU is still subject to density restrictions unless your city has its own ADU ordinance or pilot program in effect on your lot.

Start by learning basic money skills and personal finance and keep doing what you're already doing (learning about real estate!). 

The goal is to buy or build at a basis that creates equity day one and gives you breathing room.Lane two is a value add buy and hold, basically a BRRR style deal where 40k may work in the right neighborhood.

I’m learning real estate investing and interested in property research, rental comps, and basic deal analysis.

You have tried the basic steps that make sense.The best solution is re-route the water lines through a heated space.

Here is a recent post of mine that addresses your questions:Cost Segregation - The Basics (biggerpockets.com)You don’t need to complete it before the end of the year to use it for your 2024 taxes.

Basically own residential RE with the effort and risk for the same return as can be projected long term for the passive S&P.  

Basically structure a deal where the seller gets 70% from my lender and I finance the 30% with the seller. 

Basically the current LLC will first deed 50% of the property to you and the other 50% to your partner as tenants in common.