With a history of 50/50 parenting, it is unlikely his time will be reduced unless you can prove he is dangerous to the kids.

If you go to court for a modification, the child support will be adjusted to your current mutual incomes. Your allegation that he is selling drugs to supplement his income is meaningless without proof, like a criminal conviction.

You have the right to modify the custody agreement be prepared for the fact you might wind up having to pay more child support. There is a good possibility you won't .. I agree talk to an atty and find out what your rights are and what the lay of the land in your area is .. the best case scenario for you is that your ex winds up going to jail for something stupid. Now as far as him interfering with your visitation .. that you can move forward .. that has nothing to do with child support. What does your parenting agreement say in terms of visitation? If you are entitled to visitation and he's stopping it the courts can view that as something called parenting alienation. Now my understanding is that sometimes the judges will and can adjust child support based upon how much you are spending time with the kids. It's going to depend on your state and what the status quo is .. documentation of how much you are spending on the kids when they are with you .. and I'm talking basic care stuff .. and what kind of financial burden that creates for you. I'm not saying you shouldn't pay child support it's suppose to be set up so that it is an equal split again that's going to depend on your state. DO talk to an atty. ALWAYS know your rights and ALWAYS document. Hugs and good luck :)