reg. your question2: there is no real difference in terms of responsibility. However, a C3 is in principle the last step before Manager, so the expectations are already a bit different, eg. be a team lead for a substream of a project, which would less likely be offered to a C1 (obviously depends on project/size/budget etc etc). My advice is to push as high as possible. As the categories tend to be rather strict, it will be highly unlikely that in the case you are really performing well, to be promoted from a C2 to Manager. ->just see it as a possiblity to get promoted earlier.good luck