Business tax write off?

They would be write offs for 2019 when you file your taxes in 2020.

AND ...depending on what you buy you may be able to depreciate it over several years

You can start amortizing them when you actually open for business. This means you write them off over a number of years, not all in one year.

No. Equipment and other assets can't be depreciated or written off under Sec. 179 until the date they are placed in service. If they are purchased in 2019 but not placed in service until 2020 they will be reported on the 2020 tax return filed in 2021.

For the stuff that doesn't depreciate you have to write it off in the year you bought it. For the big ticket items these are probably depreciated over several years so you get partial write offs in both years.