My general advice is to start small and let the campaign grow as you and your players get used to it and discover what you really want to do. There is a reason that a small dungeon and village is often the first place games start in! They're easy to run!
I want to emphasise this - my current Loudwater campaign is the first one that really followed this advice, starting with a well-detailed little township plus local dungeons and events, and it feels by far the best and most 'robust' I've ever run. It's really easy and effective to build outward organically from that starting base, following the inclinations of players and GM. I think it definitely beats the heavily pre-plotted approach.
I think having a cast of well-detailed local NPCs from the beginning helped hugely, something I've tended to skimp on in the past. And the open, somewhat sandboxy feel lets players focus on what they find interesting, so the GM can build on that.
Wish I had your job...Im going to start planning out the campaign while at work tomorrow

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.