When I asked Topaz support that same question about a year ago they responded that
both will work and both methods are acceptable, but in general Topaz recommends running their software the last.
If you do choose to run the editing/color grading, etc. as the 1st step, make sure to export the video at the highest quality possible, Lossless compression is preferable. that way you ensure that Topaz has the most video data to work with.