I have looked through your assumptions and thought of ways to complete your work.
If the diversion of 300 points is referring to just plain weekly exchange rate changes, it is relatively easy to model your strategy using few "=if formula" on a spreadsheet.
Alternatively, if you are referring to cumulative changes from transaction to transaction, i.e. buy/sell if 300 points change after the last transaction is made, the formula gets a bit more complicated. At first, I thought that I must use a macro to model this, but after playing around few minutes with excel, it seems that it is still doable without using macros.
I can definitely separate the master variables for you to revise it from time to time. What I also think would be useful is separating historical exchange rate data tab from calculation area, in case you want to revise it. This way, you will be able to revise the data more easily and even use it to forecast estimated return by entering your forecasted datasets.
After modelling is done, the work would be nearly finished as finding weekly historical exchange rate is just a few minutes of work.
I am readily available by email in case you have more instructions. I expect to finish the model in an hour or two.