Where to connect tristate pin of oscillator?
You are correct - leaving it open will enable the oscillator.
One way of covering your bases is to put a resistor in your PCB but don't stuff it if not needed. In this case, it would be between the tri-state pin and the positive power supply.
Putting such a component in the PCB also allows you to wire something to that point if you need to test it or to modify the operation of the circuit - if you just leave it as no-connect there will not be a pad to wire to.
In general, it is good practice to use a resistor if you ever need to pull a signal up to Vcc or down to ground, it provides flexibility in testing (for example you could disable the oscillator to inject another signal for testing) or easily modify the circuit.