Network topology and 67 km link

So, I got to the point where I have no expiriance at all and I do need a solicitaion from all of you that went trough with this.

As breaf as it can get, my ISP (a new one) is assigning me /24 IP address space. Now, as always, there is BUT and this BUT is that ISP is 67 km away. So, what I need to do is to deploy a link, wireless one. For, the time being, this link will involve 4 points:

ISP → (A) – 27 km → (B) – 26 km → (C) – 14 km → (D)

From the point D, the internet will, eventually I hope, be distributed to its users.

The wireless link is not an issue here (it is yet to become one). What I am having trouble with is making my mind up on the logic of the network and I need you to give me your oppinion. We all agree that there is a phisical connection and that each point can communicate with the next one. The best option that I am having in mind here is to put a plain VPN inbetween point A and D and to bridge them and bring my ISP at point D. Egg.:

1). Assign address 10.1.1.0/30 to points AB
2). Assign address 10.1.1.4/30 to points BC
3). Assign address 10.1.1.8/30 to points CD
4). Execute VPN, where A is server, and D client
5). Bridge VPN client on D with the existing interface towards ISP
6). Create cross links from each A, B and C to D trough, let’s say L2TP for supervision purposes
7). Set a ruting table on D: 0.0.0.0/0 trough “whatever_address_VPN_server_has” gateway

… and here is where I got lost. From the logical point of view, points A-trough-C no longer exsist and it’s only left for me to assign IP address space … How? Where? I’m totally lost here.

Anybody? … Please!