I had all of our snow equipment serviced, our bags of salt were all stacked nicely, and snow shovelers were lined up.  

I can rent some equipment and demolish the old building myself, but what should we expect to spend getting a concrete pad poured, wiring and plumbing run the 100 ft or so from the main house, etc? 

Remember you have to pay for everything, including but not limited to: HOA/CC&RsProperty Taxes/InsuranceAll UtilitiesCable/InternetFFE (Furnishing, Fixtures and Equipment)Property ManagmentBooking/Payments SystemsEtc...Apologies if this is redundant info for you but most of the time once you plug in the numbers (especially HOAs) you will start to get a much clearer picture on actual return possibilities.  

I feel much more equipped moving forward than I did an hour ago.

I feel so ill equipped for tomorrow but it is a learning experience at the very least so I am not going to consider it a loss of time if it doesn't end up a good deal. 

Either it will take forever with DIY equipment or you'll risk ruining your work with the pro sanders.

On a job that size you could ask for a small mobilization fee or front end your first pay application to cover the equipment costs. 

My bank account isn't as well equipped for investing.

Her equipment is more up to date than other companies in the area also.

It is pretty simple stuff, just wear the right equipment to protect yourself.