Sites and Services Advice needed

Hi I have a few questions about sites and services etc.

Here is what I am about to do....

1. Set up a VPN between my branch office and the main site.

the main site ip / subnet is:

192.168.x.x /16

2. Join a server at the branch office to the domain over the WAN VPN

I then promote it as a DC and add DHCP , DNS etc..

the ip / subnet is:

192.168.x.x /16 (Same as the main office)

I could change this to a different subnet if required..

My questions are:

if I created a site called Branch office in sites and services at the head office, what type of link would I use? I want the computers at both sites to be able to communicate with eachother, ping / intranet etc and allow users to log in using their AD credentials at the branch office.

how would I instruct the computers in the branch office to use ONLY the DC that is located in the branch office and not the head office ones? Do the computers need to be added to a site specific OU? THIS is where im getting slightly confused because once I add my branch office PC's to the domain what is stopping them from going through the VPN gateway and getting their DHCP and DNS from the head office..

and ofcourse I also do not want head office PC's trying to log in using the branch DC as that would be slow..

would really appreciate a bit of advice here as the Microsoft docs are a bit confusing when trying to explain sites and services to my small brain.

Thanks in advance.