You're not meant to have rolling subs in Div 6 and above but usually it's done by mutual agreement between teams before kick off.
Exactly.
Div 1, 2, 3, 4, 5, 6 are for "serious" players. Div 3 is targeted at youth players stepping into senior football for the first time (but often doesn't work like that) while Pressies is for players with one foot in the grave.
Masters is for players with both feet in the grave but body still alive while Masters 45's is for those with pre-mortem rigor mortis.
Obviously a crook ref when you played Coastal! The protest for playing unregistered players/illegal aliens is already underway.