Belousov-Zhabotinsky reaction: questions about rate determining step, k and activation energy
I realise your homework was probably due a LONG time ago but I just stumbled across this.

In answer to (3) yes, the reaction is notoriously sensitive to a wide range of conditions and stirring is one of them...when the system is stirred faster (probably generating a vortex) oxygen is more readily available to react with radical species in the reaction - effectively these will react with oxygen rather than the bromide. As such the bromide in the system is above the threshold level for oscillations to occur - if you were to slow this down again then you'd see the oscillations resume.

Also I don't get why they'd make you use cerium sulfate...everyone knows ferroin is better.