Consider going to a smaller fan maybe 100cfm; it will run cooler due to lower static pressure. Also locate the fan at least 5' away from the stove and duct it to your original contact point. Pushing 300-400cfm through the 4" duct over any significant distance will put a decent load on the fan causing it to run hotter (don't know the length of your run).
As far as safety, can't comment without seeing entire setup; just clean dust out of the setup at least 2-3 times a season.
As far as safety, can't comment without seeing entire setup; just clean dust out of the setup at least 2-3 times a season.