I operate a music business to claim income and deduct/depreciate gear purchased and used in service of the business. This year (2019), I have made a down-payment on a substantial purchase that I will not complete until 2020. I operate on a cash basis and normally, I would pay for and begin amortizing the asset within a single tax year. How should I claim deductions and declare/amortize the asset in this case, since I will have costs in 2019, but will not own the asset until 2020?
You start depreciating an asset in the year you place it in service even if the payments are made over a span of many years.
How do I deduct the payments made before the asset is placed in service?
You don't ... payments are not deductible only the cost basis is once the asset is placed in service. This is a basic accounting/bookkeeping rule so you may wish to seek local assistance to get educated on this and other bookkeeping situations for your business.