This is one for simulation and some guesses on the strategy to used e.g. is it best to always get the bonus every turn or do the most combinations even if it doesn't use up all the letters every turn.
You don't need to definitively prove your answer is the highest (which is way too hard) just come up with a reasonable answer using a particular strategy
Defining a strategy (such the following) would reduce the computing power needed: Long word: Find all the 8 and 14 letter words that are respectively 1 and 7 letters longer than 7 letter words. Determine what subsets have a long continuous net of those words together. Remove those that use more of the individual letters than the Scrabble set allows. Finally lay the net on the board as a standard one player game and determine the score.