New to roll20

I am testing out roll20 and going to use it to run multiple adventures with my Edge of the Empire Group. I signed up for mentor so I have access to the full API stuff. My question is what is the best way to handle campaigns. I want to load the dice app. Character sheets. And maybe make some stuff also. Should I make one campaign and all my adventures go into that OR do I make a campaign per adventure. IF I do this how do I create things that are usable across different campaigns?

As to your last question, as a mentor you have access to the Transmogrifier which allows you to transfer different items across your campaigns. The other questions are a bit more tricky and can depend on what's the most comfortable for you. Many people run long games in a single campaign, but you should be aware that information adds up. Having a ton of pages, lots of journal entries and handouts, and a long chat log can eventually cause the campaign to slow down considerably. You can get around that by archiving items you aren't using and even clearing your chat log from time to time. Some folks prefer to keep an intact campaign for reference and either Transmogrify items they want to keep to a blank campaign or copy the existing campaign and clear anything unnecessary out of the copy. I hope some of that might be useful to you!