If you wish to program the EV3 with Scratch, then check out this project on github:
This software is a so-called helper app, that interfaces between the Scratch 2.0 offline editor and the Lego Mindstorms EV3.
The EV3 must be booted from Lejos (http://sourceforge.net/p/lejos/wiki/Home/), requires a ...
Mitch Resnick at the MIT Media Lab is the developer of both Scratch and the original Mindstorms programmable brick, and the original Mindstorms programming interface was very similar to Scratch. If you have one of the original Mindstorms Robotics Invention System sets (and a PC of the proper vintage on which to run the software) she would probably find it ...
No. Bluetooth on the computer you are using is necessary but you don't need a wifi dongle for either your computer or the ev3. If you are using the EV3+Scratch extension on scratchx.org, all you need is the scratch x plugin and a computer with Bluetooth (or a bluetooth dongle).
Here is a good article about how to set everything up.
Scratch for LEGO Mindstorms EV3
One way is to use the open-source online programming environment Open Roberta Lab: http://lab.open-roberta.org there is also a wiki included for detailed information. Or just google Open Roberta at wikipedia.
Everything is for free.