@oxzhor First off welcome to the Rockstor community.
Others here are more qualified to comment on your hardware questions but I can say that the parity raid levels of btrfs ie raid5/6 are not considered production ready so they are not really an option for your here. Even more so at the size of storage you are planning on. Please see the following forum thread for more info on this:
That is certainly the hope, given the raid5/6 caveat. Of course there is never a guarantee but btrfs 1 and 10 are your only choices here. This all assumes you are to use the raid controller in HBA JBOD’s mode. Again there are others far more knowledgeable in the forum so hopefully you will gain some more feedback in time.
Please also see the Pool resizing section of the official Rockstor docs.
I know there are others here who also use Rockstor with LSI controllers but not sure if that exact model is represented.
Hope that helps.