OK the first 4 things that you need to do....Read, Read, Read and then Read. After that, read some more. Then watch some of the YouTube videos on "how to" EVA armor. There are a ton of them. And just so you know, it is never too early to begin working on a suit. I would start on a small section first just to get the feel of how to do things.....If you have a hand plate, start w/ that. Or even a boot....either one of those are relatively easy to get your feet wet with. Now an exacto knife is great for doing detail work, but I would advise against using it for every cut. The blade is a bit short and you run the risk of running the handle top across the foam and damaging it. I would suggest a craft knife that the blade extends. One of those "Break Away" blades. They have them in either thin or thick widths. I would also recommend getting a kitchen knife sharpener. Otherwise you will be going through blades very quickly. Foam dulls the edge after only a few passes. You'll feel the difference w/ a sharp blade over a dull one when the foam starts to catch and the edges look "torn" rather than cut.
Now there are a ton of other tips and tricks I can get in to but it would take too much time to get in to one post....especially since they posts are already up here. So it goes back to READ!!!! Welcome to the 405th and if you have any more questions or need help just give a shout. There are a ton of people here that will offer assistance. Don't forget to post pics so we can see your progress and comment.