pcb isolation voltage
Yes, the standard FR-4 will withstand several kV between the two sides.
On the same side, make sure to mainain a creepage distance of at least 3.2mm for basic insulation and 6.4mm for reinforced insulation. Such creepage distances will withstand at least a test voltage of at least 1.5kVrms. Make sure to test the board when you are done.
The test voltage should be applied between the logic (low voltage) part of the circuit, all connections shorted together and the high-voltage part, again all connections shorted together, for 1min.
If you do not have a tester that produces AC you can use a DC voltage that is √2 greater than the required AC (typically it will be 2121 VDC).