In theory. The ban is not a law, however. It is the equivalent of an Executive Order so it may not be illegal.
The same one led by the likes of James Comey who targeted Trump? Nice excuse but it falls flacid and weak.
No, but she did have authority over the capitol police(or at least suggested as such.). So to me, the failure to give the Capitol Police the tools they need is something I'd focus on with the commission. It's more meaningful than finding a Trump "smoking gun".