Configure Firewall with transparent proxies

Hello,

I use [Windows Server + Wireguard], I need a solution, to let client traffic go via

..................................................................................../---------------> [Proxy1] <---------> ClientA
[Windows Server + Wireguard] <-----> [Linux Router] <------------> [Proxy2] <---------> ClientX
....................................................................................\---------------> [ProxyN] <---------> ClientA

1. [Windows Server] should receive real Client IP (proxy should be transparent);
2. iptables scripts must have some documentation/comments, so I would be able to change IP/add new [Proxies];
3. iptables scripts must have some documentation/comments, so I would be able to create/setup [Linux Router] from scratch;
4. Traffic is coming over specific well-known ports (7777, 2106, 80, 443);
5. [Linux Router] should be hidden, and accepts connections from [Proxy]/[Windows Server] only;
6. [Windows Server] should be able to initiate HTTP/HTTPS connections to the internet (via router+proxy?);