I'll throw out some things that may or may not help, as I'm still pretty green at SH5 and am still getting used to it -
1. I'm using CCIP's Command Keys mod - really helps ease the transition for SH3/SH4 vets:
http://www.subsim.com/radioroom/showthread.php?t=162661
2. Hit the ESC key while you're in the sub pen and you can change all of your realism settings before setting out on patrol. Once you have a target locked in your peri/UZO view, you can turn the TDC on/off by just telling your IWO to do so.
3. Fuel and battery levels are missing as far as I can tell. I'm using the "report max range" option in the Command Keys mod to tell me this info. Very dumb omission to not have these gauges IMHO.
4. You can turn external camera on by pressing F2 in the Command Keys mod. Not sure about the "next target" function...I haven't found it anyways.
5 Anecdotal evidence suggests that the shadows are big FPS killers. I've turned my down and I did notice an improvement.
6. As far as German voices go, I don;t think you can do it other than selecting the option upon initial install.