1) Read your contract, employee handbook, etc..
2) Read your contract, employee handbook etc..
3) What are they willing to pay? $150/hr is more than double your rate was as an employee. Is it more that they will be short staffed or that they will lack people with the skills to complete the work. If they lack people with the skills, they might pay that premium but I still think it might be a stretch. If they will just be short staffed $150 is likely higher than they'd be willing to pay, overtime for a $65/hr employee would only cost them a bit over $100/hr.
4) How much is the free time it would take away worth?