1. Assuming you mean you're curently in a Type IIA, the IID becomes available to the 1st flotilla in Sept 1940. The Type VIIC becomes available in March of 41. You may want to transfer flotillas in order to upgrade sooner.
3. Each ship sunk or airplane shot down awards you renown. See this post for renown values in GWX:
http://www.subsim.com/radioroom/show...9&postcount=11
4. DiD means "dead is dead". If you're playing a DiD career, that means that you don't reload an earlier save game if you get sunk.