What you have presented is a well researched and thought out piece of work.
One or two suggestions to improve it further.
Don't express figures to too many decimal places. On page 5 you have rate of reaction
given to 9 dp. No more than three can be reliable.
There is no need to repeat the whole list of safety precautions or apparatus more
Why not start with more dilute solutions to give you a longer time for the reaction?
In this way the last few results will not be so close together. Remember that
the reaction is not completed when the cross disappears. You are only timing it
up to a certain point. This is important to realise, because the reaction rate
slows as the reaction progresses. By measuring it early you are in the straight
line [part of the curve.