Hi,
1) The only reason why Corona Bitmap exists is to allow us to add new features (as we cannot extend C4D native bitmap), for example udim support. That being said, unless you need some feature not present in native C4D bitmap, there is no need to prefer Corona Bitmap over C4D one. Right now, there can be some performance differences, but those should go away as we optimize underlaying shader system...
2) That is good idea and should be quite simple to do, we will try to add it in next daily build...
3) This should also be possible, but it might take some time as it needs some additional internal changes, I will add it to our feature requests.
Cheers,
Aleš