That seems like a reasonable approach to me however it really depends on the rate of change in your environment.
One solution you might consider is to have an OCUM alarm which can have a script attached to it where you can call a WFA workflow that will automatically increase the volume size when an OCUM event is generated.
Seems reasonable, however be aware of some wonky behavior in OCUM 6.x/7.x that is not documented anywhere. Alert thresholds are based on potential size of the volume, while the actual threshold when autogrow kicks off is based on actual percentages. See the thread below for more: