Best thing you can do buddy is search the entire 405th forum, watch how other people have tackled their armor. There are soooo many out there and YES i would highly suggest using EVA foam floor matts for your first build. Also check youtube for great tutorials. You can checkout DaFrontLineTrooper on youtube as he does some pretty good tutorials and is a good place to start. My only real real advice thought is don't wait for someone to give you a step by step by step instruction on how to do it.....Chances are it's not going to happen. Watch how the "Pros" do it and replicate what you see. Then buy yourself some foam and try your luck
The ultimate best way to learn is by trial and error.