Access 1 location with 2 networks

[dalu]

In Croatia I have an ISP that provides
- internet access (no VLAN) (let's call this network A)
- TV (VLAN 1500) (let's call this network B)
- telephone via VOIP (not sure)
no IPV6 connectivity sadly, only IPv4.

The topology is
fiber cable <-> modem <-> router
The router then has 4 RJ45 ports
2 for the LAN, 2 for the TV with separate IP ranges.

Now I bought an APU2C4 a few years ago and I'll put Opnsense on it.

There is a TV box that acts as a streaming client in IP ranges 10.0.0.0,
as noted above it's provided with VLAN tag 1500.

What I'd like to do:
modem <-> apu <-> router

- opnsense/apu should pass all traffic to the router
so that the local network works as usual

- I'd like to be able to connect from Germany to network A and network B
I'd like to carry the TV box to Germany and be able to watch that TV there by connecting to network B, which will then give the TV box an IPv4 address via DHCP
Likewise I'd like to be able to connect to network A to access cameras or storage

I'll travel to Croatia in 3 days and hopefully arrive there healthy.

Now in Germany I only have a FritzBox 7590, which doesn't have wireguard so I'll probably have to buy some hardware to put wg there, probably some Pi/Clone or put OpenWRT on a very old FritzBox Fon 5140 there.
I'll find a solution for that. Connecting to network A is not an issue from Linux or Windows.
Sadly the shop here has the cheapest hardware listed starting with 550€, which is way too much.

What I'm interested in is the Croatia setup.
If anyone has already done something like this, I'd appreciate if you shared your experience.
Or if anyone has a solution, I'm all ears.
Also if you know any cheap hardware for the German location.
This whole thing is problematic because the locations are so far apart so I can't really test the setup.
I can connect to Germany from Croatia via the FritzBox 7590 VPN and I have a server in Germany that could act as a proxy, but I wouldn't like to mess with it, aka mix private stuff and business.

My take is,
have a dyndns client on the APU router,
configure wg for each network, provide on different ports.

I'm more interested in the general theory but will revisit this thread with specific questions or write a log of what I did.

Update 0: Good news, AVM has a "labs" version of their firmware which supports wireguard
https://avm.de/fritz-labor/frisch-aus-der-entwicklung/neues-und-verbesserungen/unterstuetzung-von-wireguard-fuer-den-einfachen-aufbau-von-vpn-verbindungen/

[dalu]

I connected the box to the modem
But WAN didn't receive an IP address.
So I connected the speedport plus router.

You know what, since no one bothered to reply, I think this is the wrong forum.
I'll start from the beginning, since it's a network issue first.

[Vilhonator]

I connected the box to the modem
But WAN didn't receive an IP address.
So I connected the speedport plus router.

You know what, since no one bothered to reply, I think this is the wrong forum.
I'll start from the beginning, since it's a network issue first.

WAN is short for Wide Area network (lame mans terms, internet). You need to un-tag "Block private networks" from WAN settings and add correct routes on both, opnsense and modem.