Data Skew refers to many records being linked to a single record. As long as there's a reasonable number of records in a relationship, you'll be fine.
This records are Lookup to account (1-1) ,is there any lookup skew issue ?
No, since each record has just one related record, there's no problem.
OWD- setting is Public read only Planing to create all the record with one user (integration user) which is not part of any Role OR public group .any Owner skew issue ?
Yes, by definition, this is ownership data skew. Note that this does not affect reporting, but can affect sharing recalculation, potentially locking your org from certain ownership, sharing, and public group changes for hours or even days.
As long as you are careful to make sure the owner has no role, there shouldn't be a problem. This is in the documentation:
If you do have a compelling reason for assigning ownership to a small number of users, you can minimize possible performance impacts by not assigning the user(s) to a role.
If you accidentally add them to a role later, or create a sharing rule that involves them, you will find your org setup locked for as long as it takes to finish processing the request. Users can still edit records, etc, but administrators will be locked out from making further sharing changes until it finishes.
