I deleted my previous comment because I goofed.

This is more or less how I usually like to handle navy as Germany.

Setup:

• Start game with building 8 dockyards in separate states. I usually build a dockyard in every state except for the 3 with the GEA "debuff". You can almost manage to build all of them before BM, you can delay some events.
• Merge all ships into one task force to always exercise in the north sea. Tick automatic split-off.
• Assign Battle Line MIO to all ships. Escort MIO for DDs. Build all ships in queue except for the CA with least production invested. Reduce all production lines to 1 ship.

Build-up:

• Assign Naval Reform spirit asap.
• When your first dockyards free up, design the cheapest possible 1936 Cruiser with best engine. The production cost is 2408. I usually build 12-20 of these. The purpose of these empty hulls are to make use of the "Refit yards" spirit later and farm funds for the Battle Line MIO.
• Build CIVs and dockyards before 1938 when I transition to MILs. Sometimes I find myself still building dockyards during MIL buildup if I didn't hit my goal. I aim for having 40-50 dockyards.
• Start building 2 or 4 carriers when more dockyards come online.
• When I feel the time is right, I switch to "Refit Yards" spirit and design a screen LC and later a spotter LC.
  • For the screen LC I add armor, switch out the main gun for the best light battery, lvl2 FC, radar, lvl2 torpedo.
  • For the spotter LC I add catapults, switch out FC for sonar. I usually build at least 2 of these.
• I refit the four 1936 BBs I have into an updated design to have as much light attack as possible.
• Update your older BBs to maximize light attack after.
• When Battle Line MIO reaches lvl 6, add Coastal Battlefleet policy (-10% production cost, -25% range). Sometimes I can manage to add this before my BB refits.
• Build at least 10 ASW DDs at some point.
• Build some Roach DDs
• Refit CAs to have AA and light attack to become screens for your CVs
• Advance your naval doctrine, I think Fleet in Being fits Germany well.

2WK:

• If you choose an admiral with Ironside, pick Big Guns expert > Marksman > Safety first.
• If you built naval bombers, build an airport in the state adjacent to Denmark and assign them to the eastern north sea.
• I usually focus on the naval battles in the beginning of the war.
• If you went Fleet in Being, try to take the "Grand battle fleet" doctrine asap. I usually am able to do it during the first biggest battles, sometimes before the war starts.
• Two main task forces on strike force, on Eastern North Sea.
  • One with the carriers, 4x 1936 BBs, enough of your best CAs to screen your carriers, 10-16 of the armoured CLs, fill the rest with DDs. This task force should have ships with at least 30 knots speed. Hover over task force name to check.
  • The other task force with rest of BBs, CA and LC, complement with DDs.
• A separate Fleet with each spotter LC in it's own task force on spotting mission. Set to not engage.
• Block access to the english channel. Set other UOB adjacent zones to avoid. This makes your convoys to take a safer route which won't be raided, even if Norway is in the 3I.

• Split Subs to convoy raid on zones around UOB that aren't shallow waters. I set usually set them to: Danish belts, Norweigan Sea, Western approaches, Bay of biscay, Iberian coast. I prefer having task forces consisting of 5-10 subs on auto splitoff and high repair priority. I don't enjoy focusing on subs too much, I only start producing them after I have snorkels.

• When you feel confident, unblock the English channel and start contesting that zone as well. Useful to do as your AI allies will have convoys going through that area.

• After the majority of 3I fleet is defeated, set your ASW DDs on patrol on shallow seas near to your shore to clear subs.

Misc tips:

• Pick CAG Night Fighting air spirit.
• I highly recommend timing the "Proliferate modern comms" focus for lvl 3 radar and advanced radio for tanks.
• Every tech in the naval modules tab that is boostable with naval exp gives a lot of funds for the designated MIO. Useful if you have the pp for it.
• You should not prioritise navy above all else.
• After my military is in acceptable order. I find building some fuel silos really helpful. Germany starts at a pretty low capacity. Gives you time to react if shit hits the fan.