Yes Fab, you were :-)
Well, it's finished. In the end, having tried and failed at using some of the generously donated code snippets, I "went back to the drawing board", sat back and thought - "Right, what do I need to do and in what order?". I then just coded it all, section by section, almost entirely on my own (apart from with some help from FabienWang as detailed below) so I am quite pleased:
A) Created a form with 4 buttons and associated OnClick procedures, then
1) Calculated each of my 4 relevant powers using the power(X^X) function and stored the value as a string
2) Read the string left to right until I found 'E'
3) Read the values to the right of E, converted to an int and stored it in a var
4) Created a number of zeroes dictated by that previously generated int and stored them in a var (max size was 177 zeroes so easily done). I had to make a loop for that - couldn't think of a better way.
5) Then I divided the var holding all the zeroes by 9 (for billion) or 12 (for trillions)
7) Then created another loop (with the help of FabienWang) to convert those groupings from a number of zero groups into "billion" or "trillion" until there was less than 9 zeroes in the loop.

Converted it all to strings and pieced it together into Label.Captions
And the result is in the attached Screenshots.
A proud day for me. Seemingly more complex than I first thought but a very enjoyable and productive learning experience.