The Touch SPI pins are separate from the TFT SPI pins. Which are separate from the (unmounted) SD pins.
So you can just connect the XPT2046 to your Nano via the voltage dividers. The XPT2046 ChipSelect is labeled T_CS. And not worry about the TFT (or SD)
Personally, I would link all the devices to the same bus. After all, you a Touch is not much good without the TFT (or SD). However, this means you MUST ensure that the unused SPI devices have their CS pins high (unselected).
David.