What is the best way to implement such a network on Microtik?

Question

Mikrotik

There is a recently assembled LAN with two offices located at a distance of about 1 km from each other. It was necessary to combine these grids with each other and add the ability to remotely connect mobile workers (PC4) to the internal grid. I didn’t work with Mikrotiks before, but I managed to get them almost for free. Tell me what to read, preferably with specific examples at the level of "copy-paste-a little_correct-everything_works" in order to ensure the efficiency of this scheme.
You want PC4 to see PC1, PC2, PC3 and ServerBox, and PC1, PC2, PC3 and ServerBox to see each other. There can be many mobile clients (PC4). It is also desirable to provide the ability to remotely configure all available Mikrotiks (well, except for R1 / R2).
Digging towards VPN tunnels and PPP-L2TP. It turned out to raise the tunnel between Lan1 and Lan2, though nothing is visible beyond the internal interface of the partner.
As always, everything was needed the day before yesterday, and yesterday it should already work ...

Answer 1

I don't see much of a problem. How many simultaneously simultaneously remote clients will be?
VPN rises to R1 (for example, I use OVPN), R2 and distribute the config to clients (login, password, keys and certificates as desired). Routing is configured from the VPN network to LANs (on R1 and R2) and that's it. Only
I would swap M1 and R1, the first one will be more interesting for the hardware (I can be confused, look
at the specs )

Answer 2

Need PC4 to see ? what does "saw" mean?

Answer 3

@iCmac
R1 and R2 - providers? does yours mean M1 and M3? What external IPs are on them (white, gray?)

Answer 4

If your routers see each other without NAT, that is, they can ping each other at the addresses that are hung on the interfaces towards the provider, then:
1. if you have the same subnets, and the addresses do not intersect and you don’t want to change them at all: raise EoIP.
2. if you have different subnets: raise GRE. Register routes to remote networks or enable OSPF for convenience.
If there is NAT between your routers: On M1 we raise an l2tp server to which both remote Mikrotik and any remote clients can connect. l2tp uses UDP as a transport and easily passes through NAT, unlike PTPP. Register routes to remote networks or enable OSPF for convenience.
Looks like I didn't forget anything.