There are already several STM32 discovery boards that are great tools for learning and prototyping. They have programming/debugging part already included also all pins to access and couple additional things like buttons and LEDs. If you need more you need to use breadboard and wire jumpers or simply make daughter boards with your desired peripherals. But if you really keen dive in to learning ARM Cortex microcontrollers and still want to use discovery line then take a look at Scot’s approach.
He decided to design baseboards for STM32 discovery boards. He already built three boards for VL, F3 and F4 STM32 discovery boards. They are easy to use as discovery boards simply mounts in to headers and are ready to go. Base boards are stuffed with many handy peripherals and interfaces. Among them you can find SD card slot, USART modules, CAN, I2C headers, ASPICE (analog, SPI, I2C) interface. Also you will find standard JTAG header where you can attach external adapter like J-link. Port headers are also aligned in convenient form.