Don't take this as criticism, but much of your subsequent question is based on common modernist misconceptions about the nature of Early Medieval warfare and government. Despite what the Total War games and George R.R. Martin might tell us, peasant levies really aren't a major part of Medieval warfare outside of very specific contexts, and even in those contexts, it's still rare that they be used in offensive campaigns, especially ones that would entail them being away from home for months or years at a time.

Early Medieval armies were small and professional, because warfare was largely the preserve of the social elite. At least until the Anglo-Danish wars of the 9th Century onwards, wars tended to be focused on distinct, short-term objectives. Even pivotal campaigns, like the West Saxon involvement at the Battle of Ellandun, were predicated on establishing remote overlordship over Kent and Sussex, rather than direct political control. I'll focus on England during the Early Medieval Period, in part because it's my field, and also because it's one of the few occasions where we do get peasant levies.

Prior to the Anglo-Danish Wars of the 860s onwards, warfare in England was predominantly the role of the elite. Armies were based around the gesith, the close personal retinue of warriors who were a leader's companions in battle and friends out of it. Originally, these were the personal friends of a warlord-king who accompanied him into battle and were in turn rewarded with gifts and glory. Consider as an example the band of Geats who accompany Beowulf to the land of the Scyldings in the eponymous epic: they are his 'sword-brothers' and he is their 'ring-giver.' As kingdoms expanded and consolidated, the thegns of the gesith became land-holders who held estates from the king in return for providing him with military service, with those relationships increasingly codified in charters following the Augustinian conversion of 597. As kingdoms expanded, so 'King's thegns' increasingly gathered gesiths of their own - 'thegns ordinary' who held land in return for service just as the 'King's thegns' held land from the King. These thegns were supplemented by members of the Freeman class of peasantry who owned their land outright and thus were due obligation only to the King. In practice, therefore, the 'army' was essentially a collection of multiple small warbands coalescing into a wider force.

These warbands consisted of professional warriors for whom warfare was a way of life and the means by which they achieved fame, fortune and status. Excavations of 7th Century Northumbrian warrior graves at Bamburgh showed that those interred were tall, well built, well fed individuals, relatively free from disease and buried with a wide array of trophies and wealth. Where we do see peasant levies is after the Alfredian reforms of the early 870s, where fyrdmen and their maritime counterparts lithmen become fundamental linchpins of English defensive strategy. The recruitment of the fyrd simply extended the obligations of military service further down the social hierarchy to include tenanted farmers. Whereas previously a thegn ordinary might simply have served in the gesith of another, the obligation was now upon him to raise a gesith of his own. Fyrd service was just one of many civil defence duties alongside roles such as fortress construction, road and bridge maintenance and manning coastguards or watch towers, and so a thegn would likely only have chosen the most suitable, competent and ready men to accompany him. We know from sources like The Battle of Maldon that thegns fought in the shieldwall alongside their fyrdmen and depended on them in battle, so it was in his interests to have the most suitable fighters. The Battle of Maldon also illustrates how thegns encouraged and briefed their men right up until the very start of the fighting. Similarly to the earlier armies, the fyrd was organised at shire level but was made up of myriad small warbands recruited at the Hundred or even Tything level. Evidence suggests that these individual warbands were discernible, or carried insignia or banners marking them out; in the wake of his victory at Brunanburh, Æthelstan personally congratulated the specific warband from the town of Malmesbury within the wider Wiltshire fyrd in the West Saxon elements of the English army.

The fyrd was first and foremost designed for local defence, to provide a ready rapid reaction force to deter the rapid manoeuvre warfare and diversionary raiding which had been a successful strategy of the Danes in the 860s and 870s, and thus free up the royal army for wider campaigning and bolster its manpower where needed. 'Conscription' as we might understand the term in a modern concept is unlikely to have been particularly necessary in this role, not least because a demoralised conscript is the last person you want in your shieldwall, but also because fyrd service advertised both considerable social status and opportunities to gather considerable loot, whether through interdicting Danish raiding armies, or by counter-raiding Danish fortresses in border areas.