And I can charge them an extra $50 for the electric and water usage?

If I were in charge of improving the perception of IB I would start with the pier and the beach.  

I charge $50 per day when I have to use it on a rental and it paid for itself in a couple months.

Opendoor's offer was $229,000 and Opendoor  wanted to charge me 7% on top of that for "processing fees".

There are some little things that you can do like turn it into an AirBnB or corporate housing where you can charge more.

Yes on home inspector, just make sure they do commercial and what they will charge you.

I had not accounted for this big of water bill charge - looking for way to minimize/cover this.Any help/insight will be greatly appreciated!

That said, if I could rent the place such that there was no extended gap between tenants, is it common place to charge the fee they agreed to in signing the lease?

We also charge 20% of gross but I like to be on the lesser side so that the owner makes more and we also strive to get the highest nightly rate that we can for our owners and optimize their properties for max ROI so 20% is sufficient for us at this point.

He used to charge that during the market crash... when materials are a lot cheaper and no one was hiring.