This Gallery provides a place where template makers can display their creations.
Normally, a download link to a zip file is also provided, perhaps with a note about how to use the template. (And/or a small text file inside the zip.)
One limitation is the disappointingly small size of graphic this wiki can apparently accomodate. This seems to be about the maximum width.
Click to enlarge
This suggests that the maximum safe size is a width of 480 pixels (12.6 centimetres). Height is not so important, although the above is 280 pixels (7.6 centimetres).
The absolute maximum size is a width of 500 pixels (13.2 centimetres):
But somebody clever can probably find a better method.