"To him a lot of upfront costs because these add up to about $5000."

That doesn't make them expense. That's why I use the word expenditure.

These costs need to be broken out and categorized for their tax treatment:

Supplies used in the production of the art are Cost of Goods Sold, which get matched to what is Sold, each year, giving you profit on sales. Until then, they are part of the art still on hand as inventory asset, such as wood, paint, hardware, etc. If you are new explaining this to the client, point out that the material costs are invested into the for sale items, which are still on hand; that means the value is still right there.

Tools are part of assets unless they are small cheap tools or consumable parts. Example: He might go through handheld jig saws three a year, so that makes them cheap and disposable, along with the blades as consumables. But chop saws and band saws can last 40 years, so they are going to be some class of asset to depreciate. That means the value is still right there, but wears out a bit over time ( = depreciation expense).

The same is true for shop improvements, or furniture and fittings, such as lights, shelving, compressed air systems. Still right there, can be wearing out over time.

Along with any other tax year-specific provisions, such as bonus depreciation. It all needs to be categorized.