Can outlet circuit ground wires be connected to the panel ground wire?
NEC 250.130(C)(2) Allows connection of ground for replacement receptacles to &quot;Any accessible point on the grounding electrode conductor&quot;.
How many wires per connector and size would be subject to the NRTL Listing of the device you are using, which includes the instructions with the device. It seems the smallest wire permitted by the device you show may be larger than the wire you are using.