And move all the items on the shelves together, face them (like in a grocery store shelf, everything is labels out, neat and in order).

I was thinking of using a piece a hardbacker and cover that with red guard waterproof membrane, angling the shelf slightly in towards the shower so water runs back into the shower.

If you pay all cash you will be getting a 20-30% ROI.If you do not use any of your own money you would have an infinite return.If you borrow money (leverage) your ROI can be over 100% easily.The simple answer to your questions are "it depends". 

Buildings reach a natural demolish phase unless you make new again as everything has a shelf life expectancy.

Obviously, we eat food on the top shelf and replace it with food with a later expiration date.Mike

Or maybe through an existing shelf company with an established line of credit.

Remove any shelf paper.

Since the expected life of the USA is infinite, there is no real need to pay it to zero.

Like if I buy an equipment at 100k as shelf price (ie the number you see at homedepot above/below the product) by the time I pay it, it will be 8-10k more (8-10% sales tax), so I am supposed to pay 110k out the door, but with the reseller, I can buy them at 100k out the door, mark-up 20k, and sell it to my client 120k and then charge them 132k (10% sales tax on 120k), then my checks will be distributed like 100k to supplier, 20k to myself, 12k to the city/county/state.

He is actually part of BP so you know that you'll actually top shelf education and service.