Not sure how to go about programming my dev board.

Other Hardware 3rd Party Boards
2

You have two in-place programming options.

  1. Program over serial. The '328 must have an Arduino bootloader installed which your chip has if you can plug it into an Uno and program. This requires an external USB to serial convertor (FT232,CP2102,CH340 your choice, they all work) and 3 connections: rx,tx (D0 and D1) and reset.

  2. Program with ICSP. No bootloader required. USASB or other programming tool required. 6 pin header with connections to processor required. Your use of the MOSI pin is not a problem since you are using it as an output - although the output may be active (high and low) during programming. Refer to an Uno schematic for the connector wiring.