Your basic connections would be not too different from this example...http://voodoolab.com/gcxdiagrams/01-Ped ... _AmpSw.pdf
The main differences for you would be that your guitar hits the Volume and Whammy first then the Out of your Whammy would go to the GCX Guitar In. Loops 1-4 are switching the front end effects before hitting the front end of the amp, but you will likely only need three loops. Loops 5 and 6 are switching the FX Loop effects, but you will likely use four loops. I don't believe you will be doing any channel switching so you can ignore the channel switching in that example.
Now for the Decimator... where do you want it routed in the signal path? Do you use it as two separate gates or with Channel 1 reading the dry guitar signal, and Channel 2 does the actual gating in the FX Loop?