It's not as difficult as you might think. It's already designed to hold water and to circulate it. You need to check to see how low the jets can go. If the pressure is too high, you need to change the wiring to make it low enough to keep it from harming the fish.
You will need to ensure that you get a pond pump that will work with the hot tub plumbling if you plan on using the same plumbing to keep the pond full. Test (pH, etc) the water before adding fish or plants to ensure that they wont die.
No problem. Seal up all the holes, give it the same sturdy support it would have if it were installed for normal use and protect if from direct sunlight.
It is very important to clean thouroughly first. Tub must be free of all chemicals that were used when it was used as a hot tub. When this is done, you may add water and aquatic plants, rocks, fish depending on what you would like the final result to be.
not really hard just alot of time removing heater elements and pluging jet holes. if your hot tub is contoured you will need to dig hole to accomidate shape so earth is firmly around tub so it doesnt break after water is in it