According to Super he was on the battlefield and escaped to gather the DBs. Since nothing in the OG manga contradicts it, I will go with the explanation Super gave.
Also, Gohan seemed to remember precisely how strong Goku was before he died so it's not like he has a bad memory either.
Future Gohan. He wouldn't be so stupid as to jump into battle against the androids who killed Future Vegeta along with several other fighters if he weren't stronger than them.
Yeah I'd have preferred it if SSJ1 went back to having fluffy hair after the CG instead of the detailed, spiked hairstyle that made SSJ2 near indistinguishable minus the aura on Gohan and Vegeta.
Namek Freeza - 140 million
SSJ Goku (Namek) - 150 million
Mecha Freeza - 159 million
Cold - 120 million
Future Trunks (debut) - 220 million
Post Yardrat Goku - 240 million
I'm starting to inflate the Yardrat boost a bit since Spriit Control has been shown to be a big boost in the Moro saga.
I don't think there is a set formula like that. Base Gogeta doesn't have feats to be above SSJ BE Vegeta and I doubt base Gogeta would be above UI Sign Goku even if he formed in the late Moro arc
I think it was a full power Big Bang Kamehameha either way. Gogeta seemed genuinely surprised when Yi Xing Long survived that attack, he expected it to be his end.
Probably within the year. I hope someone other than Toyotaro does the story though. Like how Boruto's story used to be done by someone besides Masashi Kishimoto or Ikemoto.