Think about it like this. If you were in their shoes, what would you feel is fair compensation? If you're not sure, do some research on what actual industry rates are for similar positions, and go from there. If you already know the person, they might be willing to help you out and take a cut in their rate, or even do it for free. For example, if I had a friend who was looking for a DP to shoot a tiny-budget film, I would gladly help them out for little to no rate. It all depends on who you know, what the circumstances are, and what you are ultimately trying to accomplish with your project. Simply be honest with people and you'll be surprised at what you get in return.
There are a ton of great resources available for free online that give excellent advice, tips and guidelines for writing screenplays. Michael Hauge is a great resource and teacher of the process. He has a website and multiple videos on YouTube. Here is one article from his website that deals with screenplay structure: https://www.storymastery.com/story/screenplay-structure-five-key-turning...
Another great exercise for learning how screenplays are structured is to read part or all of the screenplays of films that you have seen and are familiar with. This will help shed a light on how dialogue and descriptions all fit together, and it will also reveal the many different styles screenwriters use. Screenplays are very strictly formatted, but there is surprisingly still quite a bit of wiggle room available to create your unique voice and writing style. Here is a great resource for screenplays that I reference often: https://www.simplyscripts.com/genre/comedy-scripts.html
Have fun and good luck!