Question: Did Pamela Anderson's cameo scene hint at a sequel or was it a nod to the original show?
Answer: A nod to the original show.
Question: Why did Anna get so mad over Ryan killing Carly? If it were not for him, all of them would have died. All of them were almost dying when Ryan injected Carly. But after they were all release from the chains, Anna got so angry with Ryan and attacked him and said to him "Fucking asshole." It turns out that she killed her baby just because her baby didn't stop crying in the past. So she is not the type of the person who cares about people's lives very much.
Answer: She's just trying to maintain a moral high-ground over Ryan. Plenty of people do that all the time, especially in stressful situations.
Question: Wouldn't Earth's gravity cause Gardner's feet and leg to ache, given that he is from Mars, a planet with much lower gravity, and has lived there his entire life?
Answer: Any answer would be speculation at best, although it does seem likely that being on Earth would cause various pains. But it also depends on his conditioning while on Mars (for example, soldiers in the military often train with heavy packs on). The reason astronauts experience pain upon return to Earth after long stints in space is mainly due to muscle atrophy, similar to someone being bed-ridden for months. Additionally, being weightless in space with 0-g's (not zero gravity), their spine elongates and then back on Earth, it compresses back to normal, which can be painful. Gardner may not experience pain since his muscles aren't atrophied, and he may not experience spinal compression.
Question: Do we know that Michael is dead for sure? It seems way too abrupt, against character and anti-climactic for him to have died in the manner alluded to in the film. Or should we assume that not seeing his corpse or hearing 100% confirmation of his death means he might still be alive?
Chosen answer: Selena herself said, that Michael was dead. The actor who played him really didn't want to return to the role.
Answer: Because Scooty was nervous and didn't want to see it. If he wasn't the one that did it, he more than likely would have been curious and watched it with his mom.