My ex and I used to share custody of the kids and in April I gained sole legal and physical custody of the children. He has supervised visitation with the kids approximately once a week. I would like to move to Texas and was wondering what should I do to prepare to present this to the court. Thank you!

Tell the court the reasons you want to move that are favorable for your children. Like you will have a better paying job to support them better or whatever. The court CAN if they want to
Make the order to give the other parent visitations on holidays and summers or something as long as your ex doesn't fight it. But with supervised visitations you might have to have grandparents or somebody else where the kids can stay.
Basically, figure a way to work it all out and then go to the court tell them what all ideas you have on working it out and ask what all options you have as far as their rules go.