I know short answers are frowned upon on this board, but I think this one can be covered briefly. Yes, soldiers were expected to supply their own gear until the Late Republic (note the levy of capite censi by Gaius Marius c. 107 BC). In the earlier to mid Republic (see Servian reforms), the army was specifically organised on wealth, ie. the equipment you can afford determines your battlefield role. So a poor person might just be able to afford a shield and javelins, so they would work as light infantry and skirmishers. A wealthy landowner could afford a helmet, greaves, shield, spear/sword and a breastplate/chainmail, so he would be a principes. By the Second Punic War this system of dividing battlefield roles had been replaced by one of age and experience. So the front line now, instead of the poorest citizens, were the youngest (hastati), the 'spine' of the army would be the older more experienced infantry (principes) and the oldest most experienced men would be in the third line, the triarii. While triarii were equipped as hoplites and the hastati and principes equipped as the sword-and-board wielding legionaries we all know and love, there was some overlap of wealth classes in these groups. Some hastati and principes would have worn crappy bronze chestplates, some would have had mail coats. Naturally, the older principes would have more wealth, so more of them had mail coats than hastati.

So yes, soldiers still supplied their own gear in the Middle Republic. No, they were not required to buy exactly the same gear, but they did need the same armament or they could not fulfill their assigned battlefield role. And of course yes, there was a minimum standard, or once again they would not have been able to fulfill their battlefield role.