Sounds like a plan. I can't see why this wouldn't work.
Get a stages/power tap power meter and you won't need that cadence thingy. It will make rides like next friday a walk in the park cos for the first time ever, you will be able to pace properly.
You are riding a 26 inch wheel bike into the head winds of Victor? Hats off Andrew!
Id use silicon, tape and zip ties. That way no doubts it will hold.
FWIW, I bought a bunch of these off ebay: http://www.ebay.com.au/itm/300816351401
Then put one of them on the back of my pedal spindle - it keeps itself on fairly strongly (hasn't come off, even on rough dirt), and is more powerful than the stock magnet, meaning slightly greater distance between pedal and sensor is ok.
Yes, these are the go. Have used them for six months, and never had a problem. Neods are one of the strongest magnets available.
What i have done with all my bikes is drill and tap 3mm same as the wheel magnets and with a small drip of loctite screw in never to come out.