I usually start from '39 in Flotilla 2 or 7 for the Type VII boats. I don't use a realistic career length as I'm part of a group and need to keep my career going as long as possible. If my Kapitan dies then I start a fresh career from that date and carry on, haven't been able to make it to '45 yet as I've tried out many mods and combinations of mods until I settled with GWX 1.03 and updated to 2.0 and hopefully soon to 2.1.
I'm thinking of starting a second side career just to get more time in on this great simulation.
I do use SH3 commander as it adds a lot of different factors that make it very interesting like having to replace crew that get killed by "partisans"
or are transferred.