@karletttoThere isn't a specific format or template for posts unless the GM of the particular role-play you are joining declares otherwise. Whatever your style of writing is should be fine! =] My only suggestion if that you find a color you like and use that for your dialogue so it's easier to find and read. For example you could do orange -
"Hello, Welcome to the Guild! or a custom color
"Hello, Welcome to the Guild!" This is a great site to help with HTML color codes
htmlcolorcodes.com I personally always use standard orange as it seems to be the least used on the site. Having a unique color allows other players to remember who is who easier as sometimes just a user name or character name can be forgotten.
You're formatting looks great! As far as number of characters, again, it depends on the RP and GM. Some RPs allow you to have multiple characters others don't. If you choose to do multiple make sure you discuss with your GM how you will be posting! Also, I would use different colors for dialogue for different characters to help differentiate them. Almost all RPs come with their own custom Character Sheet or CS as you will see it named, be sure to adjust your characters to these sheets so they will fit in the role play.
There are a lot of RPs currently available for those topics! Usually a GM will post an interest check under the interest check forum of each type (Free, Casual, Advanced etc.) Once that person gets enough interest they'll make an official RP where players can start posting Character Sheets. As an example, I recently put up an interest check of my own
here. You are welcome to join it if you'd like or just observe the process, the official RP should be up in a few days.
Role-Plays that are either in process or still accepting applications will have three tabs the first being IC (or in character) the second being OOC (Out of Character, most conversation happens here as well as character sheets waiting for approval) and finally Characters where once approved you can post your character so it's easier for yourself, your GM and your co-Role-Players to find.
For your last question, the GM doesn't have to approve your posts before you submit them, only your characters. Again, the only acception to that is if the GM requires it. Occasionally if you are having lengthy back and forth dialogue with another character it helps to take the conversation to private messaging then have one or the other post the conversation as one post. It's not a rule, but it's helpful to the other players in the RP.
Hopefully that answers your questions! Sorry for the lengthy response.