No worries don,
i very much appreciate your honesty and understand your focus on single player only.
In which case i will try to help you a little with some general advice for single player only.
(obersvations made after approx 300 hours of single player campaigning with the CPs).
1. you are not the only one that finds potzblitz hard. in fact, i think playing it with the CPs in single player is one of the hardest games i have ever played.
one could say this is realistic - it must be hard to change history - and in addition the challenges the CP are facing seem to be pretty realistic.
I keep trying and trying and most of my attempts fail as well, but its still fun to see how long you can survive tha chaos.
2. Aufmarsch Ost is the easiest plan. a few weeks ago i explained in detail how it can be executed, its somewhere in this forum. germany strikes east allows you to focus on one front for a very long time as defending against france in only 4 hexes is very easy. at the same time gbr joins very late due to no belgium neutrality violation. if you strike east, ensure that you capture warsaw, riga and vilna before winter starts. its possible! dont go for the kiev option, austrian troops are poor they should not attack, that never worked for me. never waste time to ´fully kill´ russian units in the fortresses! keep the high pace and keep marching east, the hotspots will be surrounded and run out uof supply anyway. the computer does not leave the fortress. so just surround them and keep going. cavalry helps a lot in the east, build min 4 units that form the peak of the attack. russia can be done in 1915/16, which leaves you enough time to attack france as well. The good thing about this is, that italy likes a successfull germany and ist mostly attracted to join CP after campaign in the east. chance that they join entente is reduced significantly.
3. schliefenplan is already much harder. yes, you can and should take paris in 1914. sounds impossible but its achievable by very carefully using the way you approach with infantry. basic rule is: always move as many hexes as possible into french territory. the further and deeper you can move into france, the better. never miss a hex, even if this leads to strange looking frontline. if you dont capture the hex, the french will, and it is much more difficult to get them out of the hex instead of defending it when you are in it. a successfull schliefenplan should include at least two channel ports (antwerp, rouen or calais) plus paris. if you dont get that in 1914, its over. Problem is, that the AI seems to have endless transporters that keep arriving in france and bring new troops. you must stop that from happening asap. thats only possible with german naval units in the channel. thats why you need ports to resupply asap. your abovewater fleet is too vunlerable against british dreadnought dominance, which is why you should basically build one german sub per turn in avarage starting in turn 1! this will pay off. use them to block gbr transports to arrive in france. if this is done, france can be defeated. dont worry too much about verdun and the other fortresses, they can be captured later. (too time consuming!).
4. Serbia: an early victory is vital if germany focusses on the west. with schlieffen and rupprecht, german units should only deploy against france until a decisive victory is achieved. (see 3!). this will lead to a catastrophic eastern front which must be defended by austrian troops. to have them available, serbia should surrender in the first 10 turns. my record is turn 8 serbia surrender. try to beat it

this allows you to deploy all forces to stabalize the east. if you can get bulgaria into war with events, do it! use them to block russians as well. if you cant do this, the game is likely lost.
thats what makes the game so hard - you need a good execution on all 4 frontlines (france, serbia, russia and at sea) at the same time. if one fails, you likely loose as CP.
your aim for war with serbia must be the two production cities tirana and buckarest. again, the rest is less important. you have to sneak into serbian territory and approach tirana direct where you find that single hex gap at game start above that serbian fortress. go for it! first attack on it must work! if not, serbia puts an army inside which is...not good for you. artillery must fire on buckarest supported by 3 army corps attack it as early as possible. if this works, serbia is done.
5. Rupprecht: I still could not win a game with this plan. yes, my initial attacks looks okay now. but i never made it longer than 30 turns. key problems are:
- fighting the french in the mountains is slow and does not block any channel ports. you might break the defenses in france like i did (see screenshot this forum page 80), but when you arrive in paris, the british expeditionary corps has already arrived and totally crushes the rest of your army (which will be exhausted/red).
- i always had the impression that i had to fight two armies (fra, gbr) in france instead of just one if this plan is choosen. altogether this plan is too slow, reenforcements arrive too late at the frontline as the french block the railroads with forts.
- the penalty of declaring war on swirzerland leads to an italy that joins entente. that always happend in my attempts, and they just march into germany while i am crippled by british exp. force in france. at the moment, i have no idea what to do about it.
- want a challenge? try it, i would love to see a player winning with CP using the rupprecht plan. i keep trying.
6. Basically: Every surrender of any country should be accepted immediately. i know, its always nice to "finish a country off" and capture all cities and also get some experienced troops plus capture the ports. but in this game speed is more important. someone surrender? accept! and redeploy the troops to the next frontline.
7. do everything you can to keep italy out of the war or make them join you. I never won a potzblitzgame in which italy joined the entente yet. watch the manual how you can achieve that.