Rather than having classes to choose from, Mount&Blade lets you decide elements of your past which help determine your starting abilities and equipment and acts as a sort of difficulty setting. There is no randomness to your starting stats...
Custom battles are a feature available only in Mount&Blade: Warband. You have access to armies of factions (including outlaws) of up to 200 men (25 trial) and several characters. There are 3 sliders that change the percentage of troops of each type (cavalry, infantry, archers).
Calradia is the setting of the first two Mount&Blade games and the prequel, Bannerlord. There are five factions in the original Mount&Blade and six in Mount&Blade: Warband, each with a ruler, a claimant, twenty vassals and a collection of fiefs that make up each faction's region.