How to organize a CTF?

In the context of an IT event, my team would organize a CTF (Capture The Flag). About the challenges (we’re working on them). I want to have some references on the types and levels of difficulty that we find on CTF generally. (The target audience varies from students (beginner) to security experts and regulars participant in CTF). Then for the deployment, do we should use a local server? Or a VPN? In fact, we lack experience, and I need some advices/suggestions on all organizational aspects. Thank you in advance. D3_4dl1n3