As you've discovered, you can't filter by metrics.
This is a common problem with Analysis Workspace. The general workaround is like this:
- Create a Calculated Metric using the "IF" function that returns 1 or 0 depending on whether your visits/conversions is more or less than 1,000.
- Add that Calculated Metric to your freeform table.
- Sort your freeform table by that Calculated Metric.
The end result is that all of the low-value items will be at one end of the table, allowing you to focus on the other data that are high-value. Again, you won't be able to filter by this Calculated Metric.