UniFi Access + Intercom in a multi-floor house – ask for sanity check

Hi all and thanks in advance for every response!

I’m planning a full replacement of an old BTicino 2-wire intercom system with UniFi Access + Intercom, and I’d like a sanity check from people who are already running Access in real life. A TL;DR and concrete questions are at the end, the following text is reworked with ChatGPT as english is not my native language.

Our house has two floors (EG + OG). Both floors are accessed through the same main entrance door, followed by separate apartment doors inside the house. In addition, there is a courtyard gate.

Both main entrances (front door and courtyard gate) currently have two doorbell buttons (one per floor), one camera, one speaker/intercom, and an electric strike doorlock (momentary “click”, no buzzer). The courtyard also has a large motorized sliding gate for vehicles, which I’d like to integrate later but am ignoring for now due to unknown cabling. There are also three motorized garage doors, each controlled by a simple wall push-button and a (lost for years) wireless remote.

Inside, each floor currently has a BTicino video intercom that can switch between both cameras, talk to the selected entrance, and unlock the corresponding door. Each floor also has a separate apartment doorbell; the ground-floor doorbell is wired through the electrical cabinet, while the first-floor doorbell is wired directly to the intercom.

Cabling is a mixed bag: from the electrical cabinet to the front door, courtyard gate and both intercom locations there is 8-core, unshielded, ~25-year-old, non-CAT cable. There is no Ethernet at the doors today. Pulling new cables might be possible to the two main entrances, but not to the existing intercom locations. A UDM Pro SE (running Access) and a PoE++ capable switch are already installed in the electrical cabinet.

What I want to achieve is a full UniFi Access replacement, preferably without pulling new cables. If terminating the existing 8-core cables with RJ45 and getting around 100 Mbps for hubs/intercoms works reliably, that would be fine. Both entrances should have a camera with speaker/mic, door unlock, and allow visitors to choose whether to ring EG or OG. For both floors I’d like to use UniFi Intercom Viewers (phones/tablets are fine for me, but the Viewer is mandatory for my grandma on the ground floor). Controlling the garage doors and later the vehicle gate via app would be nice, but is not mandatory for day one; garage doors at least should be easy to integrate.

• TL;DR / concrete questions: Which type of UniFi Access Hub do I need per entrance to connect the main door (1), the courtyard gate with room for the vehicle gate (2) and the three garage doors (3)?
• Has anyone successfully used old, unshielded 8-core non-CAT cable for Hub ↔ Intercom or cabinet ↔ hub at ~100 Mbps in a stable way? The door might be about 10-15m of cabling, the courtyard gate about 50m...
• Best practice for EG / OG call selection: two physical call buttons / doorbell cams per Intercom, or one button with call routing?
• With one apartment doorbell not wired back to the cabinet: is there any UniFi-native way to integrate this switch without pulling new cable?
• Any real-world pitfalls when using UniFi Access hub relays to parallel existing push-buttons for garage doors or a sliding gate?

Anything here that is technically possible with UniFi Access but painful or unreliable in real life?

Thanks a lot for reading and your help!