When integrating pullets, I found that they managed better at night time than at day time. So I used some fencing ... what you have pictured here is perfect, to divide the run in half. Setup their own food and water and let them share the run. At night time you have let them come back...
My pullets were in their isolation coop for less then a week when raccoon and fox were checking them out (didn't even know we had fox nearby until it showed up on the camera). I never saw evidence of any serious attempt to try and breach their space. But, that raccoon climbed up. So, I'm glad...
If you don't have one, an inexpensive trail camera is a great buy. Even if you don't need it now, it's good to know what predators are around and what they're up to.
I'm pretty ignorant on this ... but the pictures at Cackle suggest that darker colors are better.
https://www.cacklehatchery.com/product/cinnamon-queens/
I'd suggest taking a look at @Rancid Crbtree 's build.
https://www.backyardchickens.com/threads/my-coop-design-and-build-blog.1612130/page-5
You'll find a similar style run as what you have that got completely overhauled into a more solid structure. That's more than most people would try to...
A lot depends on what you coop is like. Most coops get pretty big. For that weight to sit properly, the foundation needs to level. Otherwise, things will start to shift and crack. Pictures of the ground, coop/plans might help.
Yes, things are very stable. I have the door frame strapped/screwed to the top of the arch. Plus, I cut off the bottom horizontal line of the cattle panel so that the vertical pieces spike 4-6" into the ground.
To not use a base, I got the idea from Blooie's run...
My hoop run has no base. It's held in place only by the T-posts. I used cattle panel for (bottom section of) the other walls as well. The door frame is just 1x4's sandwiching the cattle panel framing. They're up off the ground to reduce rotting.
In some ways, cattle panel is very flexible...