Nagato takes this
-BT can in fact be used to stun and bring forth the full BM Hachibi. It was able to bring a massive rock from the water whilst pushing/attracting Naruto into it with ease. I see no reason as to why the Hachibi would remain unaffected by it, meaning any TBB attempts are sensed and countered accordingly.
-TBB's are easily absorbed, there's no limit to the amount of chakra the user can absorb according to the databook, and the manga never imposed any restrictions to it so I have no reason to believe otherwise.
-CQC isn't necessarily in Bee's favor despite having a far greater destructive capability and a more durable body. Nagato will still not die from direct hits whilst using his Asura path defences, and will have the ability to cut off the tails with minimal difficulty using Asura's mechanical parts. Using Preta path in CQC is also a terrible situation for Bee, since Nagato's ability to absorb has proven to be far more efficient than Samehada's, absorbing his entire v2 shroud quite rapidly.
-Whirlwind can be a ***** though, but it is unlikely going to kill him given he uses the Asura body/attempts to stop the rotation with a concentrated ST. A single Deva ST was capable of breaking the bones of three similarly sized toads, I don't see why a much stronger ST wouldn't be playing around with the Hachibi, even if it isn't doing massive damage.