How many LAN ports should an industrial computer have? Does it matter whether the network chip is Intel or Realtek?

Count LAN ports by the number of networks you need to separate, not by the number of devices. Most projects need at least two: one for the control network (PLCs, drives, robots) and one for the office network or server. Separating them keeps office traffic from delaying the control network and makes firewalling easier. Add ports when: you have GigE cameras (each high-rate camera ideally gets its own port), a redundant network, or the machine acts as a gateway between several lines. The chip does matter. Industrial machines commonly use Intel controllers (i210, i211, i226 and similar) because drivers are stable on both Windows and Linux, with jumbo frame support and precise time synchronisation (IEEE 1588 PTP) on some models. If your software needs TSN or PTP, check the exact chip on that model. Speed: 1 GbE is enough for control and monitoring; 2.5 GbE or 10 GbE for high-resolution cameras or large data transfers. In vibrating locations, choose machines with M12 LAN connectors.