Regarding paragraph formatting, I believe this post outlines the technique you are looking for. As noted there, the good news is that the built-in Markdown compile formats are all set up for it, you just have to make a couple of adjustments to tell the compiler that’s what you want.
With special characters, I presume you mean anything that LaTeX would take as syntax? The standard approach is to use backslash escaping on anything you need to print literally that might be taken as syntax otherwise, so \% in that case.