There's nothing problematic about this, except that it's GPL plus conditions. AFAICT, only the second condition would be in addition to the GPL, but I didn't spend much time thinking about it.
Yes and no. While the author can specify an attribution notice, the GPL limits it to being relayed amongst “appropriate legal notices” - these typically appear in an EULA or About screen. Otherwise an “inappropriate” attribution requirement could be misused to prevent modification of certain parts of the work.
As for the issue with CC, GPLv3 gives a 30 day grace period for rectifying violations which obviates many potential troll issues.
Not in a uniform way - the license distributed with the code on github doesn’t have the extra conditions.
At this point I’d nuke the repo and force push with AGPL license instead, that seems a better fit.