What is the best option for creating a VPN?

Question

VPN

Hello.
Unfortunately, I have never dealt with networks, so the questions will be slightly primitive.
I read the description of what a VPN is, but everywhere it says superficially: it's cool, set it up and use it. And the basic principles are somehow hushed up.
There is an office DMZ network built on a router from Cisco without external IP addresses. Internet access through the landlord's NAT.
There are external servers with real IP addresses. All external ones also have internal addressing.
Required:
Connect the office network with external servers so that the external servers are visible and accessible in the general office network.
Questions:
1. Where should I install and configure the VPN server? On an office router or on a remote external server. I suspect that it is remote, since the office network does not have external IP addresses for clients. So remote?
2. Is it possible to configure a Cisco router as a client so that it forwards the network to external servers and minimizes VPN settings on each computer in the office? That is, configure the router as a client, and it automatically routes to the desired external computer via VPN.
3. If we implement point 2, then schematically it looks like: the router logs in to the server, receives an IP address from the internal subnet of external servers? That is, with one side he looks at the internal network of the office, with the other he looks at the internal network of remote servers?
4. How to avoid one-sidedness so that I can get through from both sides?

Answer 1

@Falseclock
1. yes
2. you can. You don't need to configure anything on the computers.
3.correct 4.configure
routing correctly