Hey there and welcome to EN World!
Having the books is useful. You can make do with the SRD in a pinch if you are still trying to get funds together. The SRD is all the basic rules, including a lot of stuff from the DM's Guide and most of the monsters. But the SRD does not have basic advice on how to run a game. (If you need a link to one or more SRD's ask!)
The number one rule for being a DM (GM, Storyteller, Referee, Narrator, etc) is to have fun. You are another player at the table with a slightly different role. Namely the role of the rest of the campaign world. You are responsible for the NPCs, locations, challenges and all that stuff. In some ways, this is the most fun role! You aren't tied down to one character and concept. You get to be the bad guys and the good guys and the indifferent guys. You get to conceptualize beautiful or terrible locations. You get to think of the riddles and puzzles. You get to do a lot and it can be overwhelming.
So another good tip for a beginning DM is to start small. A small valley with mountains and a river (or lake) can give you a lot to begin with. You can have caves with horrible beasties; Lost mines; Problems with the river or lake; Travelling merchants and minstrels and gypsies; a corrupt/helpful local lord; a local church; the local tavern/inn; the not so distant wizard's tower; and a plethora of other things. Of course, you could also use an island. Just keep it somewhat localized and have fun with making it a place the players and PCs care about. That way, they always feel like they are making a difference and they are motivated to help the locals. Worry about the huge world building and global travel later on. When you are comfortable with the big travel, you will begin to make adventures for that travel.
Have fun. I mentioned it already, but it is worth repeating. Sometimes being the GM can seem like a chore. Don't let it be!
Have a passable knowledge of the rules. But don't be a slave to the rules and don't waste too much time looking something up. If you are having trouble locating a rule or understanding the rule, make it up. Then write down what you made up, and what you had trouble with. Look it up later, after the session. If you don't like the rule as written, use your made up rule. Just be consistent. One thing you can do to slowly learn the rules is look at the monsters you want to use. For example, if you know you are planning to use wolves to threaten the village and the PCs will drive them off, then take the time to lookup Improved Grab and Grapple before the session. Both of those options can be important with wolves. There are a lot of rules in D&D. Rely on the help of the other players and take it one little bit at a time.
Be creative! The more creative you are, the more creative the other folks at the table will be. The same goes with enthusiasm. This is why it is important to have fun. When you are having fun, you are enthusiastic.
Ask questions here on EN World. We like to help people be more successful with our hobby. So don't be afraid to ask. Feel free to join in other threads too. It doesn't matter if you are new. Many of the threads don't deal so much with specific rules related issues, except in the Rules forum. Most threads are more general in nature. Share ideas, offer your opinion. The only thing different about you is less experience with the game. That doesn't make your ideas and contributions any less useful or insightful. So don't be shy. Be confident like the great budding DM that you are.
