You start with the fair market value on the date your mother died. This can be established by an appraisal.
You can add permanent improvements you pay for, but not minor repairs that are part of selling the home (cleaning, painting etc.)
Certain closing costs from your sale will be allowable adjustments to the basis. They are listed on page 8 of publication 523 and include the real estate commission and some (but not all) taxes and fees associated with the sale. https://www.irs.gov/pub/irs-pdf/p523.pdf
Staging expenses are an allowable adjustment (considered a selling expense as "advertising"), but only as long as they do not make any changes to the home itself. In other words, renting furniture and moving it in and out, without changing the home, is an allowable selling expense and adjusts the cost basis. But painting, changing light fixtures and so on, is not staging, and is either a repair (allowable adjustment) or a repair/maintenance item (not allowable adjustment).
HOA fees, property taxes, insurance and utilities are never** adjustments to cost basis. Property taxes for property you own are deductible on schedule A as an itemized deduction, subject to the overall $10,000 cap on deducting state and local taxes.
Note that if you get a 1099-S for the sale, the IRS is going to try and match that to your tax return. So while the ordinary way to treat selling expenses is to reduce the selling price, it confuses the computer and may result in a letter. Assume the FMV is $250,000, the selling price is $270,000, and you pay $9000 in allowable closing expenses. The IRS will want to see you report a selling price of $270,000 and a cost basis of $259,000, instead of a selling price of $261,000 and a cost basis of $250,000. It all comes out the same in the end.
(**If you carry investment property for more than 1 year, you may have the option of capitalizing certain carrying costs into the cost basis. But this is complicated, and may no longer be allowed after the 2017 tax reform--the IRS hasn't definitively ruled. But capitalizing costs does not apply in your case if you plan to sell quickly.)
