Ok, here goes...
I'm in Sacramento, California, and am somewhat familiar with the Marysville area.
1st, don't add that second box this time of year unless the bottom box is fully drawn out. The days are getting shorter now, the spring buildup season is over and swarming is so slow it's coming to a halt, so the queen is slowing down her laying.
You may add the second box, but put it on the bottom. That gives them room to move down if needed and helps with giving field bees somewhere to hang out and transfer nectar to younger bees for storing, without having to enter in thru the brood nest.
2nd, your hive is only a single box without all the frames being drawn out yet, it's too small to be doing a split with it this time of year. Concentrate on keeping your single hive strong and healthy. Keep watch on nectar and pollen stores and feed supplement if it gets low, especially around the first of september thru to the first of november.
keep a watch out for varroa mite symptoms, now is a good time to do powdered sugar treatments every 4 days to a week, for 4 or 5 weeks.
Good luck and have lotsa fun with the bees!
Living in 95901 area code near Marysville, CA