Hi Dave
Well training is always a good idea. Got to be honest I never had training in the Oven cleaning department.
We clean lots of Ovens both residential and commercial.
Get your self a dip tanks, I would not say its actually required to be a heated one as I don't use a heated one myself.
They start at about £550 for a heated one.
Get some good gloves, a torch so you can see in the Oven, a couple of scrappers, some wire wool, metal scourers and a glass scrapper.
Get some good professional oven cleaner. Not out of Sainsburys.
Probably best advice I could give you f you don't go for training learn how to take off the Oven door and removal of the glass. Ovens have several types of hinges. But once you mastered this removing the door is easy.
The scary part is probably cleaning the top of the oven where the grill element is. The removes easily from most but not all ovens by two philip screws and a clip. Some times to remove the grill the oven needs to be removed as the screws are at the back where you cant get to. In this case you have to work around and in between the grill.
Other tip make sure you wash out the oven and remove the oven cleaner residue. Professional oven cleaner can be toxic and contaminate food
Hope it helps
Dave