Assuming that there are no 'unusual' items that come up, what kind of disruptions can one expect when moving a domain between registrars?

I understand some of the below may vary over registrars. But assuming both ends are large proficient registrars:

a) Will the NS settings be mirrored? We use a dedicated dns service provider so we are not using the originating registrars name servers. All that we are concerned about is that the existing NS values are mirrored at the target registrar.

b) Are incoming domain transfers automated on the target registrar end? Eg: If we begin the transfer process during business hours at the source registrar, will someone have to manually approve the inbound transfer (most likely during their business hours) at the target registrar?

c) Is the domain ever 'in limbo'? At any time in the process is there ever a time when the NS values for the domain are not populated (as they were prior to initiating the transfer) OR one does not have access to populate them (at the target registrar)?

Thank you kindly for the help.