Email conversion to yahoo questions

I have an email for the main Account on Comcast and then 2 additional emails.

 I got an invitation to convert the main account email but not the additional ones yet.

if I convert the main account email now, will I lose access to the secondary emails?

 I have a phone number associated with the main account and 1 of the additional accounts, do you need a phone number tied to an account to move it to yahoo?  
once an account is moved to yahoo can I then add that phone number to the account still on Comcast that didn’t have a phone number?