No

Yes

until the user had clicked on something or initiated another process

As long as a user can read it.

flashing on and then off is fine. The user will see it.

It's best not to, users rarely go past the first screen, and if they do it is just for a few lines if they can see that it's a continuation of what they are reading

It does not matter, people are used to scrolling down. This will not be a problem. They are used to finding completely new information on following  screens. The number of screens isn't important.

Yes, up to 3 screens is OK. and it's fine to add new and different information below the first fold. But any more than 3 and we will lose our users.