why it is a bad idea if this movie is a sequel to Gojira 1954

I like that they use the original Godzilla canon, its only that one film though and thats it.

I doubt it will have any connection to the original film. Everyone in the trailer look as if they've never seen or heard of Godzilla before, except for Watanabe's character. How do you keep a massive disaster like what happened in the original film a secret?

The 1954 stuff is probably just an homage to the original movie. Nothing more.

But to answer your post's question, I think it's a bad idea for the reasons you've already stated. Most people will have not seen the original film and adding on the history would alienate a broader audience.

I don't know how to answer the second question, but I can answer the first one.

Godzilla is ICONIC. Why make a "sequel" to a film that is 60 years old? Have you heard of "The Return of Godzilla", "Godzilla 2000: Millenium", "Godzilla vs Megaguirus", "Godzilla, Mothra, & King Ghidorah: Giant Monsters All-Out-Attack", "Godzilla X Mechagodzilla", and "Godzilla: Final Wars"?

Those were all sequels to the original film. "Final Wars" came out exactly 9 years and 3 months before today. Remember, that was a sequel to "Gojira (1954)". Does it matter that the first movie was made 60 years ago, given the fact that there have been 6 non-Showa sequels to it?

Think about that for a moment.

these is a diffrence to those movies than to this movie, those movies were made in japan, i'm pretty sure there are more japanese people who have watched 1954 compared to america

if you read what i said the majority of the audience who will watch this movie will not have seen gojira and you can't force everyone around the world this movie shows in theatres to watch gojira

It's not a sequel so there's no cause for alarm.