Help needed in combining separate listings into variation listing

I apologise for the long post but I am at a complete loss.

I have slippers in 3 sizes.
Currently they are in separate listings but I want to combine into a variation listing so that the customer can select size from a drop down menu.

The Help on this is woefully inadequate. The instructions bear no relationship to what you get. For example, Help says

To access the Variation Wizard follow the below steps:
On the Inventory link in your Seller Central account, select Add a Product.
In the List many products via bulk upload option, select Add a Variation using Variation Wizard.

But there is no ‘List many products via bulk upload’ option.
There is a ‘Create variations using variation wizard’ which I select and then the option to ‘Create a new variation family by combining existing stand-alone listings in your catalogue’

But again - this does not give me a wizard for doing it but instead these instructions:
Download the appropriate category template for your category using the Product Classifier or Templates for Specific Categories.Refer to the Valid Values tab in the template to see what variation themes are available.Note: If no variation theme is listed, you cannot create a product with variations in that category.
In the inventory template, create parent and child SKUs.
On the parent item:
Enter values for required fields, including SKU.This can be any alphanumeric string of 40 characters or less, but must be unique (i.e., must not duplicate any of your other SKUs). Sellers often append “-parent” to their base SKU to remind them that this is a parent SKU.
Leave Parent SKU field blank.
Enter a value of “parent” in Parentage and enter a valid value in Variation Theme.
Leave Relationship Type blank.
Leave all other non-required fields blank.
For each child item:
Enter values for required fields
Fill in the Parent SKU field using the value from the parent’s SKU (this value will be the same for all child items).
Enter a value of “child” in Parentage and enter “variation” in Relationship Type.
In the Variation Theme field, enter the same value that you entered for Variation Theme on the parent (this value will be the same for all child items).

So I download the template for slippers, do the above, upload it back - and get the error:
Image missing

So I edit the template:

1. I enter the folder path and filename for an image from my C: drive and upload it again

Processing, Amazon still says there are errors:

1. Your media content could not be downloaded from “http://C:%5CPictures%5CSlippers.jpg”. Due to repeated download failures from “http://C:%5CPictures%5CSlippers.jpg”, please move your media content to another hosting provider, such as Amazon Web Services S3 (https://aws.amazon.com/s3) or CloudFront (https://aws.amazon.com/cloudfront).

2. Brand (E), Product Name (H) missing

3. Size missing

4. So I cannot upload a file from my C: drive? How do I upload images to one of those alternatives? (My entry in the template begins C: not http: which is why Amazon cannot find the file on the web - but how come it was changed?)

5. Brand is not column E and Product Name is not column H. These are actually columns C and F respectively. So I enter the required values for the Parent (as the child items are already setup), even though the instructions above makes no mention they are required.

6. The slippers are suitable for a size range - 5-7, 8-10 and 11-13 so how can I enter just a single size for the variations in the template? The individual listing for the slippers already has these size ranges set correctly

Support have been less than useless again. Not even answering basic questions like how can I upload an image direct from my C drive or why do the column letters given to me in the processing report not actually refer to the correct column.

A day wasted on what should be a fairly simple task.