Tasmota would probably be the right drop-in firmware for this. It already does what a power strip needs to do and much more.

because this is part of a bigger project and I intend to add an external SPI port for analog and digital IO expansion, I have however decided to go with the following:

• Platformio
• Arduino STM32 framework (sans the crappy IDE)
• The ArduinoOTA library for OTA firmware support
• Standard MQTT client to talk to the world.

The firmware is very simple and is available on github.