Thronic

Sorry, I haven't used CloudDrive nearly enough to be able to tell you whether your plan is actually sound (I use DrivePool and Scanner a lot more) though that may change in the near-ish future.
"Drive Usage set to B only having duplicate files." - Have you tested that this works with a pair of local pools? If so, it should also work with a local+cloud pool pairing.
"Is read striping needed for users of Pool C to always prioritize Pool A resources first?" - According to the manual the answer is no; regardless of whether Read Striping is checked it will not stripe reads between local and cloud pools, instead it tries to only read from the cloud pool if it can't read from the local pool. However, I have noted forum posts about issues with getting DP to prioritise correctly, and I don't know if those issues have been fixed since those posts as I haven't dug through the CloudDrive changelog recently. https://stablebit.com/Support/DrivePool/2.X/Manual?Section=Performance Options.
The rest of your plan seems sound.

Issue resolved by updating DrivePool. My version was fairly out of date, and using the latest public stable build fixed everything.

To be blunt, when talking about storage, it's a good idea to take things with a grain of salt.  There are a lot of misconceptions and myths that get perpetuated, even by smart and experienced people. 
Worse, is that some things may have been true at one point, but technology and the like improved, but people still believe what once held true.
That said, StableBit Scanner polls SMART data once a minute, by default.  And you can configure that interval, if you want.
As for the stuff mentioned, unless you have a bad drive (either failing, or poorly designed), I don't think that this is actually an issue on modern drives, and the issues mentioned are an exaggeration. 

It's just exaggerated. The URE avg rates at 10^14/15 are taken literally in those articles while in reality most drives can survive a LOT longer. It's also implied that an URE will kill a resilver/rebuild without exception. That's only partly true as e.g. some HW controllers and older SW have a very small tolerance for it. Modern and updated RAID algorithms can continue a rebuild with that particular area reported as a reallocated area to the upper FS IIRC and you'll likely just get a pre-fail SMART attribute status as if you had experienced the same thing on a single drive that will act slower and hang on that area in much the samme manner as a rebuild will. 
I'd still take striped mirrors for max performance and reliability and parity only where max storage vs cost is important, albeit in small arrays striped together.

It's just exaggerated. The URE avg rates at 10^14/15 are taken literally in those articles while in reality most drives can survive a LOT longer. It's also implied that an URE will kill a resilver/rebuild without exception. That's only partly true as e.g. some HW controllers and older SW have a very small tolerance for it. Modern and updated RAID algorithms can continue a rebuild with that particular area reported as a reallocated area to the upper FS IIRC and you'll likely just get a pre-fail SMART attribute status as if you had experienced the same thing on a single drive that will act slower and hang on that area in much the samme manner as a rebuild will. 
I'd still take striped mirrors for max performance and reliability and parity only where max storage vs cost is important, albeit in small arrays striped together.