Your thoughts on Burn-in and Vibration Testing

Hi All,
I have some products that I'm trying to improve the reliability. The products range from assemblies with 1 PCB 40mm*40mm to assemblies with three 100mm*250mm boards stacked together.
I'm thinking of doing some burn-in and vibration of these PCA's and assemblies to remove the infant-mortality components and interconnect assemblies.
So my thoughts were:
Step 1. Burn-in stressing of the PCA's after receipting into the store. 
Step 2. Vibration stressing of the PCA's. 
Step 3. Makeup the PCA assemblies ie the three stack of boards. (Significant labor assembly content at this stage)
Step 4. Burn-in stressing of the Assemblies. 
Step 5. Vibration stressing of the Assemblies.
All of the PCB have some kind of integrated circuits. Ranging from a single sensor interface to a 676 pin FPGA (BGA)'s.
Some PCA's can be powered up as individual PCA's, others required the assembly of the three stack PCA before power can be applied.
So what are your thoughts on:
1. Temperature to use?
2. Constant elevated temperature for 1 week (duration as an example only)?
3. Cycle temperature between ambient and Max Temp, say every 4hrs for a 24hr period ie 8 cycles? 
4. What about vibration stressing.1 Axis or 2 or 3 axis? G Force level.
At the moment, I only have a large industrial oven. No environmental chamber (Big). So I can only heat.
I could get a freezer to put the PCA's into?
Recommendations on a vibrating table? for PCA's etc.
Thanks,