I haven't filed a claim all these years but insurance is for the what-if and to be used for the high-ticker items, but chances of damages exceeding the 5% is low.  

Look at insurance and tax costs, those two items are the biggest killer of cash flow.

At the end i will add a list of items why adding a single ADU in single family zoned areas may not be the best RE option.The most common value add is via a rehab.  

A savings to put deposits and another account for everything elseyou don't need separate bank accounts as accounting software will classify all of those items.

I think negotiations on knocking the price down on inspection items on value add will be huge especially if its a flip like you mentioned.

Also, what others have said, the personal touches on what is in your place (e.g. providing all the essentials instead of having people buy TP, coffee, shampoo, etc.) and the quality of those items (no tattered towels, stained sheets, etc.).  

When it comes to assessing maintenance costs, one of the best approaches is to request itemized breakdowns for larger repairs.

In my area (near the beach) its mostly families and they want cabanas, baby items, chairs, coolers etc that we do not provide but I have a local vendor that delivers and picks up these items and charges a few dollars per day for each item, and give me a 20% referral. 

It would cash flow nicely.One item to plan for from the beginning is the exit. 

I would try to buy properties starting at a specific date so not large ticket items come up.