Trimmed or untrimmed is ultimately up to you. Untrimmed takes more time, but I've heard that people often have to trim armor to fit them even though they bought it "trimmed." That would probably depend on your body size and the body type the armor best fits. I am not a very hands on person, but I bought an untrimmed set and was proud to spend the time working on it.
You should email the armor makers directly. Some of them have waiting lists, so as soon as you decide on armor you should contact the maker.
EI and Centurion are awards that you can earn by meeting mroe detailed armor requirements. These requirements may take more time or more specific materials, but I am really proud that I made my recent ATA build to EI level. The CRL's include what your armor needs to have for Entry Level, EI, and Centurion.
I hope this helps you some. Best of luck!