Specular input, from 0 - 1 maps to base reflectance in 0-0.08 range. Pretty sure you can read up online on how to convert reflectance to IOR and the other way around.
Base color is not changed in any way and used as is. Unlit mode is not showing basecolor.
What you are artistically referencing to as fresnel, is an effect, caused by many separate factors, where actual Fresnel reflectance is only part of it. And it is not something that should be subject of customization in any way. There surely are ways to create your completely own fresnel, at which point it will stop counting as fresnel. But why, especially when your work is all about real materials ?
Indeed I can and that is perfectly fine. Being feedback section, one can expect some disagreement with your suggestions.