The process sounds reasonable to me, but I'd say you're already headed in the direction of exactly the kind of shoddy evaluation process I alluded to in an earlier post. You are not seriously proposing to base a major business / technology / development decision on a collection of forum posts are you?
One way or another, it sounds like you're going to need to build expertise in a certain product within your organization and that you're going to need outside help to do it. It also sounds like you're at the very beginning of the process.
Given that you're going to need to hire consultants in any case, do not take existing products off the table. It is very likely that your needs are not so unique as to warrant the very creation of an entirely new system. Again, there are many mature and stable products already available whose sophistication a new system simply will not equal for many versions.
Draw up your specs, and send out your RFPs, but don't rule out existing systems unless you have extremely strong, specific reasons. There is nothing at all that you mention in the initial post in the thread or in your follow-up post above that can't be easily achieved with any of several mature products.
It's quite possible that at the end of a thorough evaluation process, you will decide to 'roll your own', but given what's already out there, it's awfully short-sighted to decide to do so at the outset.