I know people who have done exactly what Matt wants to do - talented people who know their own capabilities, and know that they will put the effort into making a go of it. They have been willing and able to get a limited but adequate amount of good equipment from the start, and they have had pro photographer friends who are happy to help.
Matt, if you want a reasonably well-considered, complete and appropriate answer to your question we need to know a little more about what you wish to do - what level you are pitching this operation at, the sort of work you want to do, whether or not you are confident enough to get the best from the start, and roughly what you are willing to spend.
It's a matter of striking a balance between the amount of effort you would like others to make, and the amount of effort you make in helping them to direct their efforts appropriately. For example, you and I might have very different ideas of what a 'professional grade portrait' is. Could you give links to some examples on the web?
Best,
Helen