Words that start with 'ope' and contain 'a'

What is the best score you could get in Scrabble using this list of words that start with 'ope' and include 'a'?
For a score of 16 points in Scrabble, it is possible to use 'openbeak'.

Is there a specific word from this page which could be considered as unusual?
The most stand out word based on expert opinion is 'operand'. It is defined as "The symbol, quantity, or thing upon which a mathematical operation is performed; -- called also faciend.".

Is there any word on this page that sticks out as the most common?
There's 'operation' which ranks as the 3651^st most common word.

How many acceptable words are possible to put together using this combination of letters?
You can pick from up to a maximum of 75 entries which address your query.

What is the longest word you can derive with this list?
The longest word constructed by Dictionarypedia is 'operationalistic'. It is made up 16 characters.