Congratulations on starting your own business!
If you are not all that techie, then you will need at least some level of ongoing, low-level professional support after the initial setup is complete. So you should look at this as one of the services you will be contracting out, like your paper shredding service, or your messenger services.
Figure on an initial setup fee regardless of whether it is self-managed or managed by a third party. Time is still money.
Then figure that if the system can do a lot of stuff, like collaborative document authoring, whiteboarding, chat, IM, iPhone integration, etc., then it will be (a) semi-complex to very complex to maintain, with all of the ongoing security updates, feature enhancements and whatnot and (b) a challenge to learn to use from a user (not admin) prespective.
So, depending on the level of functionality/complexity you desire, find the product that will suit your needs from a useability (not cost, ease-of-management or other admin) perspective. You can start with a broad Google (or Bing ... not that there's anything wrong with that
) search for "collaboration software" and refine until you discover a few solutions that seem appealing for you to select from.
Even an "open source" (although in this case, should probably be "self-managed") solution will incur ongoing training and helpdesk support. SOMEone's got to hold a few hands to get the top brass to fully buy into it!
I guess the short version is: Don't look so much at the individual elements like from where the solution is coming or whether you will be dealing with a charming individual or a bloated corporation, rather, look to fill your needs first, then Total Cost of Ownership over the projected life of the product (and stuff like "will it be expensive to add 100 new employees" and "how much is an average price hike when a new version is released").
You can usually find a demo of any mature product and give it a whirl. Let that be your guide.