Reviewing new IT systems

I am managing the development and installation of a new corporate purchasing system in my company. The system is being developed by a third party and will have to integrate with a number of systems, and fit with our corporate data model, with as little impact as possible.

To help limit unforeseen risks I intend to set up a technical review panel, who will critique and assess all proposals and products. Hopefully the panel can develop a procedure for such reviews, as I hope to then use them with other projects. I have no experience of technical reviews, and would like to know what areas of expertise should be included and what type of questions should they be asking?