Just got the revised starter and trying to work out some of the details: How does close combat retaliation work when the squad that is retaliating has multiple close combat © weapons? For example if the hammers are attacked in close combat, do they get to hit back with one Rocket Punche or two? Same question for Rhino, in case the answer is different.

In the rules I see two statements (emphasis mine): "…retaliate agains your close-combat attack with a close-combat attack"

And: "So, all weapons with range C can be used…to retaliate…"

So the retaliation is one attack, but uses all range C weapons available?

Yes, when retaliating in close combat, you can use all of your C weapons.