I'd expect split opinions, on this one. I've seen a number of people insist, in previous threads, that leaving the sprayed "primer" (in quotes, as we're actually talking about non-primer paint being used in the same capacity)/undercoat showing pretty much guarantees inferior results. I wholeheartedly disagree. A smooth-covering aerosol enamel, like
GW's Chaos Black spray (from what I gather - I've never used it, myself), gives a perfectly acceptable finish. With a good spray paint and proper application, the results should be indistinguishable from an airbrushed basecoat, which nobody seems to see fit to rail against.
A black base, specifically, presents its own issues - namely the inability to shade down through washes. If you're willing to highlight up, exclusively, then you should be good to go. I've done the exact same thing using ColorPlace flat black spray touched up with Apple Barrel black craft paint (which just happens to match quite well) on my Orks, which wear a decent bit of black. I've generally left the black un-highlighted as a matter of expediency, but once the rest of the model is finished and varnished, there's no evidence that I took that specific shortcut - merely that I got lazy with highlighting.
For what it's worth, I say that (at least for your purposes) the plan's a good'un.