You need a criminal defense attorney.
Offense Gravity Scores do not "add up" Each charge has its own offense gravity score. To determine the standard "minimum range" you must also know you prior record score. In addition, some charges merge for the purpose of sentencing. Other charges can be withdrawn or reduced as part of the plea negotiations.
Having an experienced local defense attorney is your best option.
Your grading does not work by adding the scores of the offenses up. If you would like to know what you are facing and what defenses you have, you should sit down with an attorney.
Michael L. Doyle