Alright so first I'll quickly hit some things that are accurate.
Weapon Rarity and Design
Swords being rare, considering the amount of trouble to get iron or steel and then to get someone trained in working it into a sword (not just a weapon, spear and arrowheads are relatively easy) the cost is huge, then add on that a sword contains enough metal for several axe heads or spear heads and at this time iron was so hard to come by that the Irish altered all foreignly introduced designes to be lighter and contain less metal, so far that a spear which would have two rivets when made by the Vikings would have one when made by the Irish. Every nut and bolt counted. Alot of it was probably imported, not so strange, most Scottish claymores used 7+ centuries from the games time would of been made in Germany or Italy and imported, infact the German's greatswords might come from them liking what they were selling to the island so they made some for themselves. Swordsize and shape is alsor pretty spot on, they were apparently a little shorter than those used by the Brits against the Romans centuries before, before the Germanic tribes and Vikings they were lighter and not as sturdy, so when the locals saw these foreign swords they copied the designs so everyone had a very similar style. Everyone also liked to copy Viking axes. For their part Vikings copied some local styles for other things, namely javelins and spears.
Land, Taxes and Military Service
Its not specifically stated but when you get your little piece of land, your fief, thats roughly proportional to having a "hundred", that is 100 hides, whereas each hide is about 10 hectares and can support 1 family (the actual sized varied, some land sucked so it was more like 12 hectares, some land was good so only 6 was needed). That would roughly make you a Reeve (old english for Sheriff), but this mod doesn't currently support a ranking and title system. As each family worked the land they made enough to feed themselves and to pay a form of taxes to an overlord person who would use them to pay for weapons and armour and to perhaps pay for underlings equipment. Germanic Kings and nobles would have personal gaurds called Housecarls, that is Housemen, who aquired all of their equipment, food and board from their lord in exchange for serving him, this makes them kind of a landless elite warrior class. Originally 1 hide was supposed to be able to support 1 thegn but after about 250 years technologies improved and prices went up so that it required 5 hides to support 1 thegn on average. These thegns were a seperate nobles class from the peasents, the only work REQUIRED of them was military. The bulk of the army was composed of fyrdmen, that is the normal peasent types, part-time farmer part-time soldier, for equipment, well most of their taxes went into the thegn or reeve's maille and axe, they got spears, a shield, maybe tough clothes. Not really that bad for the times.
Common German Tactics and Equipment
Basic tactic was the shield wall, (F8+F1) everone stands close together in a rectangular formation, shields ready, cavalry charges can't get through, arrows and javelins are so so, works best at the op of a hill or river. Of course some members would return fire, usually with thrown weapons, namely stones (cheap and affortable, realistically, rock to the head can make you plenty dead), slings (rock X 10), javelins (good for range and weight, can usually carry 2-3, 1 at the read with a spare or 2 in the shield hand, strategy as old as Rome), throwing axes (great for smashing shields, real ones also would bounce unpredicatbly so throw them down and bounce and ignore the shield, Franks used to use them in a huge volley, who needs to aim when you throw 100 axes at 100 guys in formation and then you charge them? AXES DID NOT DISAPPEAR AT LEAST UNTIL HASTINGS). Bows actually weren't that common except amongst the Vikings, who used an early type of longbow and some Hunnish style bows. Even the Britons who were famous for the longbow in several centuries did not really make use of the longbow at this time, the bows they did use to a limited extent was a flat bow (if you need the differences explained, wikipedia has an alright article, Flatbow one word). When two shield walls meet its like a shield bashing match with short stabs at legs and unprotected areas, but it is not really reproducable in the game, and it would be rather slow and boring comparatively. Its also worth noting that most of the Vikings, the so called Great Heathen Army, were better equiped and trained than the Saxons, or any other military on the Islands, these people have raided Russia (parts of which were a Viking Kingdom at this time), the Middle East (anyone who watches the Thirteenth Warrior, parts of that happened, just not the Thirteenth Warrior part) and Parts of France (which had Normandy as a safe harbour now). When they found better loot than what they were wearing they traded up, it was therefor not uncommon for Vikings to be equipped in fine Persian armours with a Hunnish bow and a huge Danish axe. They also had direct access to Northern Germany which was apparently better equiped on average than the south.
Common Briton Tactics and Equipment
Britons did not, to my knowledge, make as much use of the shield wall formation, they preferred mobility and lightness, their Irish cousins at the time barely wore anything that could be considered armour, cloaks, pants and shields which is a couple steps up from a millenia before when it was tattoos and shields. Alot of slings and javelines, light leather and cloth armour, shields and spears. In most Briton Kingdoms they liked to ride alot and throws javelins from horseback, the Welsh Kingdoms had problems with horses at this time though and so they had practically no cavalry. Spears were a popular weapon, as it had been for the Celtic people for centuries. Guerilla warfare and dawn raids were their preferred tactics, and making use of the terrain of Wales, that is hills, mountains and rivers. Its worth noting that Wales and the Brits are one of the few peoples in Europe who resisted the Germanic Hordes that conquered Gaul, Spain, Italy and parts of Greece. Thats more than enough for this post.