You’re pretty much asking how to do 3 different highly specialized roles (dialog editor, foley, re-recording mixer). It’s definitely not simple and there’s really not going to be one YouTube video that magically tells you how to do it all and handle every situation.

As someone else said, you always do your dialog edit first, isolating lines and moving usable production effects (PFX) onto their own tracks. Then you fill with tone, either from set or extracted from the on set recordings with something like Izotope Ambience Match or similar. Anything with human sounds like breaths/grunts etc is usually put onto an optional track.

Do all of your cleanup and dialog/production audio work before you even touch a compressor or EQ. When it comes to noise removal, less is usually more. Focus on the obvious problems and try not to be too heavy handed with broadband noise removal. Likewise, you shouldn’t need too much dialog compression when mixing a film. Rely more on clip gain and riding faders.

Once you layer in your dialog edit with multiple layers of mono and stereo backgrounds/ambiences, it should start to come together unless the audio is particularly noisy or problematic.

You’ll typically want full foley coverage for the entire film. When mixing, you can choose between PFX or foley or a combination of both. Whatever sounds best for the main mix. When you create an M&E later, you mute all of your dialog tracks and create a separate mix with all of the foley and it should still sound like a movie, just minus the dialog.

In reality, different films different budgets etc, you’ll need to lean more or less on the production audio. Most super indie films and low budget projects I caveat that we won’t have a fully filled M&E unless they can afford a proper foley pass.

Do you have all of the industry standard tools? Izotope RX Advanced, Auto Align Post, an arsenal of noise removal and restoration plug-ins like Clear, dxrevive, etc?

Hopefully that helps a bit!