Cleavers: They are the germans version of a heavy weapons unit and they can do well against infantry that makes use of sheilds but can suffer vs spear wielding infantry. To boot they do not really have good defense against ranged. So essentianly cleavers can be countered by spears and ranged. Although you need to keep in mind they can instantly make a unit retreat with their Frighten ability. Also if a church has been built they can use a ability called Holy Fury to decrease the defense of enemy units. Some of the abilities that the german units can make use of need certain technology tiers to be researched and some need a church.
Panzer Infantry(Spearmen): They can use their Intimidation ability to temporarily pin enemy units in place and reduce their attack damage, keep this in mind before engaging this infantry unit. They are more resistant to arrows than the cleavers. You can use Shieldmen against Spearmen but with the Panzer Infantry (Spearmen's) Intimidation ability you could afford to be careful because if your Shieldmen get pinned a heavy weapons unit can flank your unit of Shieldmen for example Cleavers and Berserkers. Heavy weapon units can be identified by the two axes on their portrait or the cleaver for German Cleaver infantry. Although most spearmen can be countered by archers.
German Archers: After tier two has been researched these archers gain a ability called Hold the Line that increases their defence and damage chance and another ability called Awareness (Awareness does not need tier two to be research for your archers to use this ability) that increases their sight and weapon range. Any ranged unit in the game is vulnerable to melee units, the preferable unit could be Horsemen(Cavalry) as archers can be faster than certain infantry. Or you could use your own ranged units againts the enemies ranged units.
Panzer Cavalry: these german cavalry units have two abilities, Fear that decreases the moral of enemy units. Also Sacrificial Craze that increases their attack damage and morale temporaly but leaves them unable to retreat. Spearmen could possibly defeat the enemy horsemen but the problem is catching the horsemen. This can be done by setting traps for the cavalry, of course you need to predict where the cavalry will go, they could go for vulnerable targets and this could be your archers or shieldmen, because they usually can not deflect the horsemens charge as well as spearmen, as almost any horsemen will not do well in prolonged melee combat.
Crossbowmen: They can be very effective against infantry but are fragile and a little slow and as such they can be a bit more vulnerable to infantry. They have the Chase ability to increase their movement speed temporarily. Also Victoriuos Spree to boost nearby allied units morale.
Also the Ballista and Catapult siege machines can be used to quickly capture enemy or neutral villages and against enemy units but for those that do not know using these siege machines can backfire as they deal just as much damage to your troops as well as the enemies.
Cleaviers can be good at defense with their frighten ability and they can use it more often when you get the speed bouns as they gain veterancy also getting their holy fury ability could increase their defensive potential. The speed bouns can also be used with other units as they gain veterancy.
You could use the Panzer Infantries Intimidation ability to pin enemy unit in place and decrease the enemy units attack damage and flank some Cleavers behind them and use their Holy Fury ability to decrease their defense or Panzer Cavarly and use their Fear ability to decrease the enemy unit moral and also can be combined with Sacrificial Craze.
Or perhaps you could use the Panzer Infantries Intimidation ability to pin the enemy units into place and shoot them in the back with Crossbowmen units
Perhaps instead you can use Cleavers and their Holy Fury ability to decrease their defense instead and shoot the enemy units in the back.
The Slavs faction could possibly be a threat to the German faction because they can get Horsemen and Archer Horsemen fairly early which they could use to harass the villages the Germans have captured. This faction could also use it's calvary to counter the Vikings village harassing by simply using their horsemen archers to pepper down the viking units although the Viking Scouts could be used to tie up these quick harassers, the infantry will need to quick so they dont escape. A German ally could be handy because the Panzer Infantry could pin the horse archers in place.
This helper I have made is not final and I hope that I can provide another one when the final version is lauched.
And I am open to criticism and I hope you find this bundle of information helpful.