This is terrible advice to give a Newbie DM.
For any newbies reading: Do not do this. Spending several months of prep before playing is a recipe for sure disaster.
Rather start small with one dungeon and one town and work up from there.
Gonna second this. HORRIBLE advice. Being a "god" doesn't mean you have to lay out an entire planet before the campaign starts.
My invariable experience with DMing is that 99% of anything you spend time developing before the game starts will NEVER see use because the PCs will run off in a direction you hadn't even considered and you end up having to do all the work on the fly anyway.
The advice I give in the system I'm writing is to start small... a single region maybe a week's walk from edge to edge; a community or two where you can restock and some dungeons you can explore. Then grow your world, region by region, as your player's explore it.
I've got a bunch of tables for newbies to roll/select from in the book for those who just don't feel like coming up with it all from scratch. Need an unplanned dungeon? Its a (roll) shattered (roll) magic academy that is important because of (roll) its ancient armory and is dangerous because of (roll; ooh... roll twice) angry dead and murderous heirs.
I also recommend a fairly sparsely populated world to newbie GMs; that way when the player's invariably go off on an unexpected tangent you can throw a wilderness/travel encounter or even a session while you figure out what's actually over that next hill where your current map ends and it doesn't feel out of place to the players.