I second the Wizardly One on making sure that you have a good BA. That being said, I know that Salesforce markets the heck out of not being software, but it sounds like you are going to be doing a lot of software development. If you already know that you are definitely doing that then make sure that you have a solid team of professional software developers. Don't go cheap. The last thing you want is for someone with no DB design experience to end up designing the entire enterprise DB (i.e., the Salesforce Object model) for your large scale systems.
I'd hire someone who has experience running designing, developing, and deploying SF projects, someone who understands team development concepts, someone with enterprise application development experience. You don't want someone who only has SF experience. They are going to need to be sharp in DB design, HTML/CSS/JavaScript, other languages and technologies (Java, Oracle, etc) for the integration. If you can get at least one really solid SF developer you can have that person help you more with hiring and training others who are less experienced.
Lastly, to echo one of Leon's points, if you are doing large scale team development it is very important to have controls in place. It is very easy and tempting to make changes willy nilly in production, but that doesn't always scale well when there are multiple large scale projects going on and/or multiple large scale custom enterprise apps in use. Here are some good references that someone leading your team development should be able to analyze (pros and cons of each) and implement:
Team Development: Possible, Probable, and Painless:
http://www.youtube.com/watch?v=EfXMY-ZFXXY&t=5m34s
Development Lifecycle Guide:
http://www.salesforce.com/us/developer/docs/dev_lifecycle/