Can I use the se. 179 deduction over multiple years? If so, do I claim the highest percentage available this year, or split it into thirds (expected life of the vehicle?

Unfortunately, Section 179 depreciation is only available for the first tax year when you place the asset into service. Any asset value left over after Section 179 is applied may qualify for Special (Bonus) depreciation. If any value remains, it would be depreciated over the remaining life of the asset.

TurboTax will help you choose the best depreciation option for your property when you enter the asset.

I have a follow-up question about the definition of "placed into service." ... If my service/retail business is cash basis and I pay for new furniture late in the year, put it in storage, and then put it into use in the store early in the next year, do I have a choice which year to take the Section 179 depreciation or must it be strictly one or the other year?

If you are not talking about inventory then the furniture is PLACED INTO SERVICE once it starts serving in its intended purpose  ... sitting in storage in a warehouse is not the intended position I would guess.