Project line offers:
An additional support slot @ lvl at 2 different points
Higher armament space
Capable to use higher calibre guns earlier
Slightly higher Durability
Slightly higher turning force @ lvl
Slightly cheaper @ lvl
Bismark line offers:
Admiral Hipper, Prinz Eugen and Bismark have more armament slots than their counterparts
Higher Displacement
Slightly shorter bodies
Easier to use @ lvl
Potentially more range due to armament space limitations
Both are good lines, but you must be patient. Project allows you to compete with larger ships earlier on using higher calibre guns, however you'll generally have less slots than the Bismark line and guns require a higher level gunner. Due to the space limitations on armaments, you'll be using a lower calibre gun on the Bismark line, however it will provide you with more range and force you to snipe and keep at range. Since it is a lower level gun, your shots should be more accurate at level than the Project line. AA capability for both lines are equal and the lvl 30 X2 3.46"/76 SK C/32 AA and lvl 42 X2 5"/61 KM 40 AA guns are the best choices in my opinion and will give you lots to do when you're more in the support role.
Personally, I find the Bismark line to be fast if you set it up correctly and you will definitelly need 3 engineers by the end of it. Doing over 50 knots in the Admiral Hipper and Prinz Eugen is a lot of fun as well as mid to late 40's in the Scharhorst and Gneisenau. The ships in the Bismark line tend to be slightly fatter which again forces you to sit behind the line and snipe and with enough speed, time your advances.
Don't bother with much armor unless you plan on doing a lot of 1v1s with certain ships or you are low enough to go into BKs. In BKs you aren't so reliant on speed as you are on accuracy and firepower and having a mediocre turning speed will drive you to put on a little bit of belt armor and bulge for those annoying torpedoes. GBs are different in that you'll usually be against BBs of higher tier that may out range you, hit far harder and are ridiculously more accurate at level so speed is key here.
Honestly it sounds to me like you would prefer the UK BB lines than KM due to hard hitting, armor-whored ships. KM lines require very skilled gunners in order to get accurate shots starting at the CA level. You can easily get frustrated having current level gunners since KM apparently recruit the blind; spread really is that terrible. You shouldn't really be putting much armor on majority of the ships and the ones that you can forgo some speed are past level 80. It also doesn't scale as well as other nations, so you're essentially blowing through most of your speed and displacement for little to nothing in return. In that case, you miss out on 2/3rds of the entire line if you're just going to burn through it. KM can hit hard, but not outright like other nations.
You have to rely more on range, accuracy, gunner skill and surprise to defeat higher tiered opponents. To get an upper hand on your opponent, you'll have to constantly be checking range, using your scout and blinding them as much as possible. A blind BB gives you better survivability after all. I think what people don't realize is that if you have skilled gunners and are great at manually aiming, you can take out a heavily armored BB5 in 3-4 salvos with 11" triples, but it really does take a lot of effort to get to that point. Good luck with finding your line however I recommend you look elsewhere for your needs.
