Drag a line out from the final basecolor node and just type lerp, which will highlight Math/LinearInterpolate, which is the one you want.
Something like that, yes. Were you not using a base material with a setup like this before? (It’s also given as an (incomplete) example in the manual.)
No, I just grabbed the first 2 textures in my list for this quick example.
They get replaced anyway by the material instance creator, although it’s good practice to pick neutral textures that won’t influence the material in any way.
A flat white baseColor texture, a “flat” normal texture, etc