It looks fine to me Maybe raise the substrate a few inches though? GBBs are pretty good climbers, but still, just to be safe
Size of cage is a matter of personal opinion. Some people like their T's to have bigger cages, others (like me) prefer them smaller (compared to the spider). Bigger cages are fine but it will probably be harder for the T to find food. Your cage looks like it will be good for that spider for a long time though
Why did you buy a tarantula if you didn't know this information before?
Does your T have a water bowl? If not put one in there, it needs water.
Also, add some plastic plants, NOT cardboard/paper products, so your T doesn't live in a prison. Do that and you will observe some gorgeous webbing from this heavy webbing species. In such a prison cell as that container, your T will always feel unsafe.
Now this is "debatable" because not everyone loves (like me) to work in little when slings are concerned. Ok. But no fake leaves, anchor point, cork bark... nothing. Only substrate. That "odd" web is, basically, a from your C.cyaneopubescens to the 'Spartan' environment you offered.
Theraphosidae are little genius and they "work" with what they have, no doubts.
But a 'GBB' deserve better, man
This is a great sp. an deserves a good environment. As others have said it, Water dish and shrubs/plants are a must for these as they need places to hide and feel safe. They make a fantastic display species, they have great appetites and have are a treat to keep.
Here is a photo of the permenant enclosure I recently rehoused my GBB to-
I hope you enjoy keeping your GBB as much as I do mine.