I have done about 5 or 6 home settings in my life (D&D, not counting other games). I feel it's quite a rewarding experience.
The one I'm using right now, I have planned it differently than what I used to do. I did my world map (well, stole one and refurbished it), stole about 13 or so city maps, and quickly described (in two pages) the overall world.
From there, I only prepare what the players interact with. So far, I have described 3 to 5 towns/cities. This way I don't burn myself out, and I can create cities according to the synergy of the players and the story line. Works great so far.
I use the PH pantheon, so that's another thing I didn't have to prepare.
I did a setting once, called Alderiz, that took me many months to prepare. I did the history of the recent 2000 years, created races, religions, countries, drawings (of the new races mainly, and of some features, such as a city in the mountains viewed from the side), maps... it was quite an undertaking. Before our first game session, I had a 50 page document.
I didn't use half of it. The players don't know everything you wrote. It doesn't make a difference from their POV wether you described every nook and cranny of the setting, they can only interact with so much.