Explanation
VCN A (10.0.0.0/16) will use a range of IPS from 10.0.0.0 to 10.0.255.255 and VCN B (10.1.0.0/16) will use a range of IPS from 10.1.0.0 to 10.1.255.255 so will not be any Overlap between 2VCNs

Explanation
Dynamic groups allow you to group Oracle Cloud Infrastructure computer instances as "principal" actors (similar to user groups).
When you create a dynamic group, rather than adding members explicitly to the group, you instead define a set of matching rules todefine the group members. For example, a rule could specify that all instances in a particular compartment are members of the dynamic group. The members can change dynamically as instances are launched and terminated in that compartment.
A dynamic grouphas no permissions until you write at least one policy that gives that dynamic group permission to either the tenancy or a compartment. When writing the policy, you can specify the dynamic group by using either the unique name or the dynamic group's OCID.Per the preceding note, even if you specify the dynamic group name in the policy, IAM internally uses the OCID to determine the dynamic group.

Explanation
https://docs.cloud.oracle.com/iaas/Content/Object/Tasks/usingpreauthenticatedrequests.htm You can create an unlimited number of pre-authenticated requests.
You can't edit a pre-authenticated request. If you want to change user access options in response to changing requirements, you must create a new preauthenticated request.
URL: https://docs.cloud.oracle.com/iaas/Content/Object/Tasks/managingbuckets.htm You can change a bucket's access from public to private or from private to public. Changing the type of access doesn't affect existing pre-authenticated requests. Existing pre-authenticated requestsstill work.

Explanation
VCN resides in a single Oracle Cloud Infrastructure region and covers a single, contiguous IPv4 CIDR block of your choice. The allowable VCN sizerange is /16 to /30