The residuary beneficiary is typically named in the paragraph in the will that says something along the lines of “I give all the rest, residue and remainder of my estate of whatsoever kind and wheresoever to…”(c) if there is no eligible person entitled to letters under subparagraphs (a) and (b) of this subdivision who will accept, the court may issue letters to one or more of the persons interested in the estate or, if any be dead, to his fiduciary.– any other beneficiary named in the will or a creditor of the estate can petition for Administration CTA letters.

You may have issues with residue in the hvac coils or vents.

Apparently, the residue from meth smoke seeps into the floors, walls, and ceiling and above a certain legal level, requires a professional meth abatement.

Honestly, it's too bad that the operating part of your dad's business does not carry with it some residual value of some sort with regards to that commanding a sale price.My hunch would be that this would be far too risky to embark on as a first go of things.Especially, from what you're mentioning this may have a large impact on the quality of your dad's retirement.If you have the funds and can structure something, the place to start would be to engage with an A/E firm to get a cost estimate generated for a concept building like you're mentioning. 

I'm thinking that a want to mainly focus on multifamily after I get rolling because of the residual income but obviously I have a lot to learn before I get to that stage. 

For the existing system:  If there is any residual value of the existing system (which it doesn't sound like there is), I believe you can deduct that residual value the year when the system was removed.  

Typically the residual land value won't allow it.

Love the idea of residual income! 

@Damien L. if you don't want to create a new business entity yet then you can appropriately track your income and expenses and then use Schedule E on your regular 1040 tax form.FROM IRS.GOV WEBSITE:Use Schedule E (Form 1040) to report income or loss from rental real estate, royalties, partnerships, S corporations, estates, trusts, and residual interests in REMICs.

The plan is to start moving towards multi family very soon to build that residual income.