If you look on Garnstudio, they have lots of dresses and you may be able to find one you like.
You need to be careful of what you knit it out of. Make sure that the material you choose meets your needs, for example alpaca will be drape, but not hold its shape. Certain wools and cottons would work best. It's your dress so your choice if you want to use something with glitter or multicoloured.
The length of time is going to depend on how complex it is and your knitting skills, as well as, how large are the needles and the weight of the yarn.
The type of needles is going to depend on what you find most comfortable to work with. You will likely also need stitch markers, a measuring tape and a way to block it.
Once you select a pattern I would recommend taking all your measurements and compare them to the pattern schematics. You can make adjustments as you work to ensure that if the pattern has a huge waist and you want it more fitted, then you can take it in more, or if the waist is to high, add some more rows, etc.