389/59/9 is an excellent way to get to St. George. You can also take 9 east to Zion Nat'l Park if you haven't been there yet.
Right now the North Rim is closed for fire activity in the area. Each national park has a wonderful website giving lots of good information on special alerts, road closures, things to do, camping, map, etc. Check them out.
Services in the park close Oct. 15 but you can still get into the park for some hiking. DeMotte campground just outside of the park gate is a nice place to stay. There's also a lot of great boondocking spots near DeMotte (the next road to the west). Just drive in about 1/4-1/2 miles and you'll see some nice spot. That time of year is beautiful for the aspen color.
https://www.nps.gov/grca/planyourvisit/conditions.htm