Sounds like you have an excellent start!! Also consider how you will handle such things as what assembler tools you will use, what part programming tools to use, and use care in making the electronics boards.

A scale application can need a very high accuracy A/D of some sort. Besides accuracy this part of the hardware will also need enough resolution, analog stability, and analog conversion repeatabilty.

You need probably more than 12 bit A/D converter because lets jsut say that you want to weigh from 0 to 100 kg in .01 kg (10 mg) resolution. This takes 10,000 count conversion resolution. Often for a scale application a dual slope type converter is a good choice. They can be low cost, 14 or more bits resoultion and simple power supply requrements.

Hope you have a successful project !!!!
Michael Karas