>> When selecting a category like Training or cafe supplies i would like it to default to the relevant account code. Is this possible?
FormsCentral currently does not support scripting/linking for you to achieve this.
Another product may work better for this case, please check the Adobe LiveCyle/Designer forum:
Alternately, you may want to try FormsCentral Skip logic feature and see if that works for you: https://www.acrobat.com/formscentral/en/library/skip.html