Short answers, pulled from the story.
Under Augustus, a Roman legionary served for 25 years. Before Augustus reformed the system, the average term of service was around 10 years. The final five years of the 25-year term were spent on lighter duties.
During the Pax Romana, a rank-and-file Roman legionary was paid 225 denarii per year. The emperor Domitian raised this to 300 denarii. Pay was supplemented by donatives from emperors and by plunder from campaigns.
A Roman legionary's three principal weapons were the pilum (javelin), scutum (shield), and gladius (short sword). He also carried a dagger called a pugio. His full kit included body armor in one of several forms, sandals, greaves, manicas, a marching pack, roughly fourteen days' worth of food, a waterskin, cooking equipment, two wooden stakes, a shovel, and a wicker basket.
Wheat made up roughly 60-70 percent of a Roman legionary's diet, eaten as bread, porridge, or hardtack on campaign. Additional rations called cibaria included wine, vinegar, vegetables such as beans or lentils, salt, salt-pork, cheese, and olive oil.
A Roman legionary found guilty of cowardice or dereliction of duty was stoned to death by his own comrades. When an entire unit displayed cowardice, the unit could be decimated, meaning one in every ten soldiers was executed. Lesser offenses could result in demotion, a change from wheat rations to barley, or removal of military insignia.
The decline began under Septimius Severus, whose lavish donatives and pay increases eroded discipline by raising legionaries' expectations of reward. Under Caracalla, citizenship was extended to all freedmen, erasing the distinction between legionaries and auxiliaries and allowing recruits of lower standards into the legions. The military pressures of the third-century crisis then shifted Rome toward faster cavalry forces, and by the fourth century infantry had abandoned much of the classical legionary's armor and had replaced the pilum with darts.