I don't know about others. I said your total gear is not enough. I never said D5k is not good enough.
For $500, D5000 works, but you need to pack a spare body in your bag. And kit lens is not enough. You will need a 17-55/2.8 or at least a Tamron/Sigma 17-50/2.8. Recommend you also bring a couple of backup lenses as well, maybe a 50/1.8 and the kit lens (if you want to keep it budget). One thing to note. Nowadays, most couples will ask you what camera you use. So be prepared to defend your choice of camera body. Better still, have amazing photos to show them it is the person not the camera (that is if you have the skill la).
For your Flash, you will need at least 2 more sets of extra batteries. So for SB600, you should pack 12 fully charged eneloops. For your cameras, you need at least 2 batteries each (I recommend 3 each). If the spare body shares the same batteries, just pack 3 will do.
And yes, your skill level needs to be there. If not, word gets around that you are a quack, it will kill your reputation. That is why it is better to wait till you are good enough before even considering offering as a service.
Hope this helps. Wish you all the best.