Options are either physics, which means JK's physics affect the thing, or path, which means it cannot be affected. It's guessed that the movesize is larger and is the bubble which triggers the explosion of the secondary mode of the sequencer charge. These determine what factors of JK physics will affect the thing. They control what .keys will be played for specific actions. This is to prevent too many projectiles or sprites existing at once which would hurt bandwidth and memory.
Flags can control a huge amount of things.
A thing's natural resistance to things like sector thrust. This is used to cut down the amount of objects in a level, freeing up memory and in multiplayer games, bandwidth. Randomizes the aim of the trailing thing. Creates a trailing thing for a projectile.