A few pieces of general advice:
1. Read the DMG from start to finish.
2. Be prepared to make mistakes.
3. Keep going forward.
4. Make sure it's fun, not just for you, but for your players.
5. Seriously - it's not just about you. If you want to create a world and shoehorn the players into it, you're better off writing a novel.
Now, to answer your direct questions:
do you create stats for every npc?
Oh, god no. In fact, I'd say I create stats for about, maybe, 5% of the NPCs that are encountered (excluding anything I expect the PCs to fight, of course).
Generally, you'll get by with just a personality trait or two, and maybe some rough idea of what the NPC is capable of. If the PCs try to kill the NPC, that's when you open the monster manual in a pinch and try to find a statblock that roughly corresponds to what you think the NPC is capable of.
Is there a good map generator somewhere for city's wilderness and dungeons, or do you simply make your own.
I make my own. For cities, I draw major roads on a piece of paper, as well as general terrain features like hills and rivers. I don't draw individual buildings, but put on the map the boundaries between major city neighbourhoods, where important buildings are, and all that.
For wilderness maps, I use hex paper, which I download online.
For dungeons, nothing beats graph paper, though I'll use plain ol' printer paper in a pinch. I make sure, when drawing dungeon maps, that they are not linear - that PCs can get through the dungeon in multiple pathways.
For all three types of maps, you can easily pinch them from online sources, modules, or whatever else. Real-world maps are totally viable, too, and at a smaller scale, won't easily be recognized by your players (for example, if you live in the US, you could easily just steal city maps from the UK or Europe and use them mostly unaltered).
I have some really good ideas for starters but may need a little insight on getting there.
Word of advice? Keep your ideas simple, and expect to adapt to player actions. Don't write out a plot outline! Saying "This happens, the PCs do X, and then this happens, and this awesome villain does this, and then this happens, and then this, and then there's this really badass fight in a burning castle, and then..."
Your players are going to make choices that will affect your plot outline. You're better off with a loose situation, a villain, and a goal for your villain.
As another piece of advice - maybe try running a pre-written dungeon first? There are a lot out there, and they often provide a great starting point for new GMs.
But in the end, just remember - have fun! And make sure your players have fun! Do these things, and you're golden.