1: Is there only prepaid scripts? If not, is it safe to use free scripts or does it have higher ban rate?
Check the script repository on the top of the page.
2: How the hell to I access scripts and Chat box?
Go to the "scripts" section, click the button "add". Open osbot and run the script?
Chatbox, just click the "chatbox" button on top of the page?
3: I got banned on my old account using another bot, and they say it's up later this month, is it the same for OSBOT?
Getting banned is not because you use a specific but, but how you use a bot. Read some things on the forum to lower your banrate (e.g. don't bot too long, take breaks)
4: If I want 99 runecrafting which bot will be the best for me?
Again search the "script" section for runecrafting bots, and see which methods are supported. There is nothing like a bot which is the best to get 99 runecrafting. It all depends on your method.
I advise you just to search around the forum and try things by yourself.