Your flash will need to be in M/Av (Manual or Aperture Value) mode in order to trigger correctly. Whether you choose to use the manual power level setting or the Av (we used to call it "auto thyristor") mode, in which the flash controls its own power level based on light reflected from the scene to its sensor, is up to you, but M/Av is the only mode that fires "dumb" from the flash's centre hot shoe contact. Other modes use different contacts.

You can use the test button on the V5 that's in TX (transmitter) mode to test fire the flash. (You can hand-hold the transmitter; the test button doesn't always work when mounted to the camera. I'm not sure why that is, but it does seem to be hit-and-miss on the D70.) The D70 should trigger the V5 TX at any shutter speed, but you might not get correct sync or full flash power above 1/1000 of a second - there's a bit of a delay in the radio circuit that prevents reliable sync over 1/1000 (which is still faster than most fire-only radio triggers), and the flash duration at high power means that the electronic shutter will close before the flash is finished firing if your shutter speed is too high.