Will Touchstones be wasted if I touch more than one before death?
Not at all. In general, touch them as soon as you see them.
When you die, you respawn at the closest position available.
So life giving amulet, touch stone or meat effigy.
The only reason not to touch it, is if you got a base besides another respawner, and you'd prefer to respawn there. You risk regretting that when the base is under attack by a giant, it kills you, and you respawn there.