It can be completely bus powered! (There is a DC jack for supplemental power input when you need to do full BW & 2x2 MIMO at high power, but pure bus power is fine for the vast majority of cases).
Yes. This was actually the original project for the GNU Radio framework. Take a look at the ATSC code. it may need to be updated, but it is a full [offline] ATSC decoder.
its a false positive, this was fixed in 3.2.*