Power: there are additional power outlets available at every group of slots. For example, there are connectors more suited to running PCI-e cards closer to the PCI-e slots below.
SATA: yes you can use them for your own drives. Third-party vendors (other than Promise) should be getting close to supplying the appropriate short cables any minute now.
USB-A: I believe that may be a USB-3.1 speed connection, intended for use inside the cabinet, but I cannot confirm that at this writing. The USB on the outside of the I/O card are only USB-A at 5Mbits, suitable for keyboards or slower devices, NOT mass storage.