Welcome from Texas. This is the right board to come to for answers to your questions. Here's a you tube from Man Sewing that shows how to make a weighted blanket & I hope this helps you. It's been a while since I've watched the video so not sure if it will answer all your questions but I think it will help. We would love to see your finished project.
https://www.youtube.com/watch?v=svqiyDlJmus