If I'm applying to Oxford, does the Oct 15th deadline also apply to my other choices?

Hi. I'm a little confused as there's multiple answers online. When I apply to Oxford by October 15th, does this also mean that I have to have picked my 4 other uni choices by that deadline too? I understand the same references, personal statement and all are sent off to the unis, but I am unsure if I have to have submitted the applications to my other choices as they have the usual January deadline.

Also, do you just send off one application? Some people say I can add a Uni choice after ive submitted my early application but I can't see this on the UCAS website.

Just a bit stressed as there's not clear info! It would be super helpful if someone could clear this up for me?
Thanks!

No, AFAIK the deadline would only apply to Oxford (unless you’re applying for a course that has an early deadline in general such as medicine).
Yes you can submit one application then do the rest later.
https://www.ucas.com/applying/applying-to-university/dates-and-deadlines-for-uni-applications#_026-entry-application-deadlines

thank you !