I'm with pop: go body-only and buy your lenses separately. Kit lenses won't provide the macro capability you need (more on this momentarily), and they definitely won't provide the wide aperture needed to ensure high shutter speeds for dog action shots.
igte is spot on that it doesn't pay to get wrapped up in the feature / MP race game. I have a 4-5 generation old dSLR and the biggest obstacle to my taking HQ photos: my own skills. Consider buying 2-4 generations old for camera body and spending the bulk of your budget on lenses.
FWIW, I've used the Pentax variant of the Sigma 17-70. I sold it, and wish I hadn't. It was an outstanding walkaround / general purpose lens. But note it's not a true macro, though it may provide sufficient close-focus capability depending on the size of your subjects. If you do have a need to go full-on macro, I've found macro shooting best with manual focus, so you can save a few bucks by buying an older, used MF lens.
For product shots, you'll probably want to come up with a light box of some kind. DIY is the way to go here, I think. Not difficult, and cheap.
Spend the bulk of your lens budget where you'll really benefit from the extra money spent: a fast (and therefore big!) zoom for dog action shots. Depending on your expected shooting distance, an f/2.8 in the one (or more) of the following ranges might do the trick: 17/18 - 50mm (Tamron or Sigma?), 50 - 135 (Tokina?), 70-200 (Tamron or Sigma?). Of course, Canon/Nikon makes lenses in those ranges, as well, but you'll pay a premium for them.
Do you still have your old lenses from the Nikon SLR? If you still have them, you might be able to use them on a Nikon dSLR. Can't say for sure, as I'm not familiar with Nikon's backwards compatibility, only Pentax's.
As with recording gear: don't be afraid to take advantage of the used market!