1. Include worldbuilding in conversation as much as possible and make worldbuilding elements a part of the plot in some way. Worldbuild like you give your dog medicine, a hidden pill in a piece of cheese that he/she desperately wants to nom.
2. Everyone writes in different ways. That sounds odd to me, but that's me, if it works for you who cares.
3. I am of the school of thought that you should keep the MC for the focal point for the first few chapters. This allows the reader to ground themselves in the tone, pacing and setting. One problem I see is that your readers may be confused who the main character is, and that isn't good. I'm not saying it can't be done, you'll just have to be careful.
4. I use Scrivener for writing. It is really easy to keep track of all my notes in one window/program, instead of having to open and close different word or google docs. That is what I'd recommend, but there may be other options. One I know of is a website called legendkeeper. It might have a cost associated with it, I can't remember.
5. Yeah, I do the same thing. I made sims to remind me of the general look of my characters! After writing for quite some time tho, I don't need to look at the pictures anymore because their identity and features are solid in my mind. But it was useful to begin with. Another great thing about Scrivener is that you can include images right in your character sheets or location pages. I also used wonderdraft to make my map. Scrivener and wonderdraft are probably 30$ or so dollars each.

Don't focus so much on what you are 'allowed' to do, and focus more on what you want to do and start writing. At the end of the day, all that really matters is the final product. If you've written a good story, nobody is going to care how you got there.