Murals

It depends on where it is. If it is a small mural in a child's bedroom, say, you could use emulsion or guache or readymix. If its a big indoor mural, use emulsion. If it is outdoor you would have to use gloss paint or an oil based/synthetic paint of some sort. If it is going to be in strong light don't use the ready-mix, get something with better colour fastness.

For most indoor jobs emulsion is good, there are differnet types, satin finish, washable etc. You can get tiny sample pots that are great for details and use the small standard tins for other parts.

That depends entirely on your style of drawing. Outlining it in marker could give you a comic strip look, without an outline would be more Disney. I would say no, but it really does depend on the style you are going for.

Do a practise version/section, one in just colour, and one outlined, and see what you think. You would need to do a drawing first anyway and put a grid on it, if you are not experienced you will find it difficult to get scale straight on to a wall.