I am not a MET, but I will give it a shot. One of the METs can do better with this question.

The inverted -v is the appearance of the tropical wave on satellite, surface and upper air charts. Best example I can find is located here: Inverted V

As for the amplitude question. Using the link above. Notice the amount of deflection (rise) in the inverted-v diagram.
The bottom line (labeled 10) would be considered a"low amplitude" wave.. if all of the remaining lines were of the same amplitude. The wave shown would be a "low amplitude wave".

However, the line marked "12" is of medium to large amplitude.
So I personally would consider the wave pictured on the link as a large amplitude wave. Mainly because it extends from 10N to 26N, in the picture. That is well over a 1000 miles.

Here is a link to a paper written many years ago by Dr Neil Frank, former Director of NHC. Who now works as a TV Met in Houston, Tx.
http://docs.lib.noaa.gov/rescue/mwr/097/mwr-097-02-0130.pdf