You want to be careful using two rounds of compression; you'll raise any noise floor through the roof.
Why do you want to keep vox at a constant level, at least to look at on a meter? It's what reaches your ears that's important, not what it looks like on a graph or meter. A compressor, or limiter for that matter, is to stop peaks that are distorting noticeably, not so a graph looks 'pretty'.
cheers, Graeme
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