You could consider offering to have the shower inspected by a licensed professional to provide a written report confirming its safety and functionality to address your tenant's concerns.If your tenant continues to refuse to pay rent, you may have grounds to evict them for non-payment of rent.

Renting the Baltimore property first might provide some additional cash flow to support the ADU project.

They don't really provide any tax benefits and their veil is easily pierced by a good lawyer....Just have plenty of good insurance.

I'm wondering if it's common for PMs to provide detailed receipts for each project, and if it's reasonable to request them.

if you're looking at 1-4 unit properties, don't kill yourself trying to create an LLC just yet. find your lender first then see if they'll require you to close in an LLC or not. single-member LLCs do not provide as much legal protection as we would like to think, so if that's your reasoning for wanting to create one right off the bat, that's just something to consider. as far as a business license, AFTER you close on the property, call the town hall and ask if they want you to have one there bc you're collecting rent there. if you're using a PM company, they will probably say no. :)

Note I am not an expert on LLCs but I pay for experts to provide us guidance. 

Does anyone have any experience with this that can provide some insight on how to structure a deal? 

He will be providing the capital to cover the closing costs and part of the rehab.

Addendum states: - Buyer to provide financing for 70%. $225 X 70% =$157,500.

There shouldn't be any need to negotiate them as you would negotiate rent, they just are what they are, and the owner is required to provide proof of those costs to you.