Quantity   Component name
1 × ST Nucleo-F207ZG or ST Nucleo-F746ZG Both are available, have Ethernet and lots of I/O. The F7xx might be an overkill and could be kept for a more demanding project, so I should start wth the F207.
1 × 8-channel DI/DO interface evaluation board I got this at a trade show in 2014 from ST. It has a CLT01-38S4 digital input device and a VNI8200XP digital high-side driver IC. Communicates over isolated SPI with the microcontroller, has some nice LEDs for I/O status feedback. And it requires 24V for power, so the next point is...
1 × 24V DIN-rail mountable power supply Ideally something that only occupies one module space. High current support is not required, it only has to drive the microcontroller board, the I/O board and the output relays.
8 × 230V DIN-rail mountable relays SPST or SPDT type, should only occupy half DIN-module space per relay and has to be driven with 24V DC.
1 × Enclosure for the microcontroller and I/O board DIN-rail mountable.