The MaxSTM Version 3
The image below shows OnStep telescope controllers built on the MaxSTM Version 3.6 PCB. This design uses the STM32F411CE and offers a wonderful balance of features and performance including the ability to operate the mount and two focusers or a focuser and rotator. It provides internal sockets for Wifi (or Ethernet) and an DC3231 RTC. It also has I/O brought out on a DB15 connector where it's easy wire other devices in, like a PEC sensor and encoders and home switches and BME280 (ambient/weather) and GPS, etc.
The case this Max series PCB is designed to fit is here: Aluminum Enclosure Electronic DIY PCB Instrument Project Box Case(120x97x40mm). The included case flat end panels can be prepared with very careful drilling, cutting, and filing to provide openings for the various connectors. Better, if a 3D printer is available the panels can be printed with little time or effort from these design files.
The very affordable EasyEDA service can be used to order this version of the PCB (or obtain the Gerbers.) The BOM with most required components is present in the EasyEDA schematic, nearly all components can be ordered from EasyEDA/LCSC, the sections below explain how to order everything needed to complete the build.
Whatever you build use an appropriate DC rated fuse (current rating depends on stepper drivers/motors/etc.)