^^If going aftermarket wheels, why not just get fitment that is optimized for the model 3 without spacers? Spacers really are a bandage fix. But, you may still need them depending on the offset and overall dimensions of the wheels you get.
Since you already purchased your wheels, best bet is to ask the vendor and other model 3 owners how they are setup (eg, post the exact wheels you have), with special emphasis on offset required for a flush look. That will be instructive on the size spacers you need.