Transfer migration using new Apple ID

Hi, I am sure this will be a stupidly easy question for most of you! We have a 10 year old Mac and are awaiting delivery of a new one (yay!). The old one was “registered” with the only Apple ID we had at the time, but since then have incorporated our stuff into a new (less clumsy) Apple ID. We would like to use the new ID as the basis for the new Mac, but I am wondering if all our data will be transferred onto the new machine under the old ID and we then end up with two Apple IDs in use on the same machine. Hope this makes sense, many thanks.