Is the walk from the subway to the museum reasonably safe?

New York City is safe to walk.

Astoria is a pretty good area, the q103 bus leaves from the 7 train at vernon blvd and passes the f train at 21st 41av. It will take you very close to the museum.

Long but safe.

You can also take the Q69 straight from the f at 21st

Yes

Yes, it's safe.