(b) Gorillaz only became a solo project starting with Plastic Beach. The debut was the dudes from Deltron 3030 with Damon Albarn, who had done guest vocals on a Deltron track, brought in as a full member (plus a few stray session musicians and such), the second was a collaboration with Danger Mouse, while Plastic Beach and the Fall were both self-produced solo albums (and were pretty meh compared to their earlier stuff).
Incidentally, Deltron 3030 basically sound like if the first Gorillaz album focused exclusively on hip-hop. This is basically the first Gorillaz song:
Here's another with Damon Albarn from the newest album:
And here's one without Albarn: