Although the tenant initiated the payment on 12/31/2024, the funds didn’t reach your account until 1/6/2025, making it 2025 income.

It sounds like you have an un-permitted unit, which is essentially always a risk since there has been no notice to the AHJ that it exists and they can therefore initiate a code case to have it removed in most cases.

If I have several options, I would prefer a HELOC with no initial draw requirements (i.e. to establish a literal line of credit that I have no specific short term plans to use), i.e. not something like the better.com HELOC. 

Update: I decided I will pay a $500-750 or so to do an initial hydro-jetting of the system. 

Initially, I thought I could split the lot.

Once I've completed these initial projects and built up some capital, my long-term goal is to transition into buy-and-hold investments in potentially more affordable markets to maximize cash flow and scale up.Right now, I'm particularly interested in investing locally here in the Seattle metro area.

I bought these two houses that were next door to each other with a partner using hard money (3pts, 13% interest, and 1% extension fee every 3 months after the initial 6 month term).

On the initial agreement, it clearly stated that the buyer was going to be using financing and listed the terms of their financing

Once you get past the initial learning curve and have some basic knowledge, it gets a lot easier though and at that point most knowledge gaps can be filled as they come up.

Recognize initial cash flow is likely at an all time worse.  3 recent studies show that the rent to value ratios are at an all time worst.