[This post is part of "Things to Consider Before Purchase" blog series.]
Creating a team to help define the critical components is extremely helpful. This allows a fresh prospective amongst the team. Having a solid group of goal oriented team members is also critical. No dead weight or sacred cows here!
Once you have a team assembled building a business case for the purchase is important. This business case shapes the direction and keeps you on track. Imagine starting a new business with no business plan. You can imagine how quickly a project can get off track.