We are not sure it is because the electricity is off so the sump pump is off, or if the sump pump was on in the first place it still would have flooded.What kind of measures can I take during the rehab to prevent any future flooding, besides a working sump pump

Period.The KPI I will typically measure for SEO are:1.

Have you read the book,  "What every real estate investor needs to know about cash flow...and 36 other key financial measures" by Frank Gallinelli. 

Are you referring to a standard property survey for measuring a lot?

You can install either multiple smaller systems or a larger, multi-headed (multi-zoned) system.Regardless of the heating or cooling system you install, your biggest bang-4-buck will come from air-sealing and improving the building envelope ... this can be a simple as replacing weather stripping on doors and windows and caulking trim to adding additional insulation to the exterior (or interior) of the wall assemblies / attic space and replacing windows and doors.You should probably start with having an energy model {aka heat loss analysis} performed on your house which will identify the current energy losses and the measures you can take to improve the performance.

We've had clients change their offered commission numerous times during the course of a listing thinking it would make a difference - our experience is that above 3% or with a BTSA (Bonus to Selling Agent) it doesn't have a measurable difference - the Buyer is generally in control and pushing a client towards one home or another based on your payday may land that agent in hot water later.

My advice though, make sure you read through reviews thoroughly and measure the dimensions of what you're purchasing.

We will pressure test the entire structure 3 times during construction and once at final turnover to ensure our air sealing measures were successful. 

Some places do a regular appraisal where somebody comes to the house and looks around and takes measurements and pictures.

In a former life I was responsible for creating a billing system for a municipal utility (customer service manager) and what you describe is somewhat common.As an investor, and separately a CRE professional, I've had to confront this issue.The cleanest way to handle this situation is to install a sub meter to measure specific usage e.g. the unit or the common areas.