Some players have asked if they can help their friends build at the prerelease because they are new and have never built a deck before. Is this allowable?

It is allowed and it is even encouraged! Do note that they are not allowed to help their new friends during their actual games.

Regular REL events (prereleases, FNMs, etc) are meant for fun and education of players, not just for competition and skills. Allowing players to help each other deckbuild helps to foster this sense of fun and education. Just remember, they can help them build decks, but not by giving them cards to use! That's still a big no-no.

A further question (that I believe I know the answer to). Because this is Regular REL, this allows for ‘continuous build’, correct?

Exactly. And it is expected and encouraged - to try out as many of the new cards as possible :-)