Regular Cast is for the main or starring cast of the series and is reserved exclusively for cast members with a series regular status per a season on-screen credits. There are no on-screen credits since the show has not premiered but most of the people you added have been announced as either part of the guest cast or the recurring cast, not main cast:

Storm Reid will guest star as Riley Abel.

Anna Torv will recur as Tess.

Jeffrey Pierce will recur as Perry.

Murray Bartlett will guest star as Frank.

Nick Offerman will recur as Bill.

Nico Parker will guest star as Sarah.

It looks like Merle Dandridge was announced as simply part of the cast, with no information regarding whether her character is part of the regular cast, guest cast, or recurring cast, so she can probably stay for now.

There have not been any announcements saying characters called "Head Stuttering Passenger" and "Mr. Adler" are part of the main cast.

If the actors announced as recurring (Anna Torv, Jeffrey Pierce, Nick Offerman) are credited as part of the main cast once the show premieres and appear in more than half of the season, feel free to add them again.

According to IMDb (https://www.imdb.com/title/tt3581920):

Pedro Pascal - Joel Miller - 10 episodes
Bella Ramsey - Ellie - 10 episodes
Nick Offerman - Bill - 10 episodes
Anna Torv - Tess - 6 episodes
Merle Dandridge - Marlene - 6 episodes
Murray Bartlett - Frank - 6 episodes
Gabriel Luna - Tommy - 6 episodes
Jeffrey Pierce - Perry - 6 episodes
Storm Reid - Riley Abel - 2 episodes
Nico Parker - Sarah - 2 episodes
Kevin Sateri - Head Stuttering Passenger - 2 episodes
Brad Leland - Mr. Adler - 1 episodes

According to this list, as far as I understand, those with 10 and 6 episodes are regular cast. Am I right?

IMDb is not a valid source.

Shall I add the recur ones as regular cast?

Shall I add these people as guests on S01E01?

Only add to Regular Cast the people announced by reputable websites as part main cast. For everyone else, please wait until the show premieres to see how they will be credited.

For example, when users go into Anna Torv's details, they want to see upcoming movies and TV shows. It is clear that these actors will definitely play in this TV show. I think these actors should be added to this TV show and if necessary this should be corrected in the future.

Not adding Anna Torv to the Regular Cast section does not mean she won't appear on the show. It simply means she is not part of the regular cast.

I think these actors should be added to this TV show and if necessary this should be corrected in the future.

If an actor is added to the Regular Cast section and they turn out to be credited as a guest star once the show premieres, the actor disappears from the Cast & Crew page if they are added to the Guest Stars section without being removed first Regular Cast first, which I've seen happen multiple times on various TV shows. This means having to remove the actor from every episode they were added to and then adding them back to the episodes. It's much easier to simply add the actors announced as part of the main cast to the Regular Cast section first and everyone else announced as recurring and/or guest star gets added once the show premieres and on-screen credits are available.

I understood what you said. I also say that let's add these actors as regular cast for now, If it is announced that these actors are guest actors, they can be simply removed from the regular cast.

I just checked the official website and it now lists all of the currently announced cast members. Based on the website, Merle Dandridge and Anna Torv can be added to Regular Cast. Nico Parker, Murray Bartlett, Nick Offerman, Storm Reid, and Jeffrey Pierce should not be added to Regular Cast as they are called guest stars.

I added Merle Dandridge and Anna Torv as regular cast. To add other actors, do I have to wait for the TV show's air date to add it as a guest actor on s01e01?

To add other actors, do I have to wait for the TV show's air date to add it as a guest actor on s01e01?

Yes. Especially since there is no way to know if they will appear in S01E01 or any other episode until the show premieres. Remember, IMDb is not a valid source.

By the way, why is IMDb not a valid source? I know anyone can add data but as far as I know, actors’ pages are managed by their agencies.

Because it is a user-contributed data source, meaning anyone can edit the information. It should only be used if there is no official information available (anymore) or to double-check information found in secondary sources.

actors’ pages are managed by their agencies.

I don't think this is true. Just recently, the IMDb page for Moon Knight had Gaspard Ulliel appearing as Anton Mogart in all six episodes and Fernanda Andrade as Wendy Spector in multiple episodes when they only appeared in one episode each.