What are the general guidelines to conduct a stress test for an assembled PCB to test reliability after fabrication?
You probably also need an oven that can maintain a high humidity, a device to generate ESD pulses, and a shaker table. Maybe a hi-pot tester, and facilities for EMI/RFI testing (an anechoic chamber and some antennas?).

Actually, you need to first write a very detailed and specific description of the range of environments where the board will be used. It's your board and you are the only one who can know this. If your board will become a commercial product there may be government regulations to be added to your list.

Then write a detailed and specific list of every characteristic of the board that you care about and can be measured. It's your board, you are the only one who can know this.

After you have these documents the rest becomes obvious.