Either. You provide your own switches. 3 pin and 5 pin will both fit*; no leg clipping needed. (I have two Preonics and have tried so many different switches in these wonderful boards)
*Use Cherry MX Compatible Switches
From what I could find out the Preonic uses the STM32F303 microcontroller. According to the datasheet, the flash has minimum endurance of 10k write cycles (page 82).
The board comes with presoldered addressable LEDs around the edge of the board, other than that there is a cutout under each switch where you could put LEDs but there is nothing else other than the hole. If you wanted per switch LEDs you'd have to wire them separately.