Lots of experts on Pond Boss, but experimental data is also very helpful.

I might buy just 200 and split them between the terminations of your rip-rap areas where you have plants growing nearby. If they decimate your plants in those areas, then you know you will need to stock in very low numbers, and far away from your desirable plants. If they do create a breeding population in your rip rap, but you only find little ones next spring when you pick up rocks in that specific area, then you can stock in higher numbers next year.

Your existing fish (plus your soon to arrive LMB) all will eat some crayfish. However, I (non-expert) think you can still establish crayfish easily if your habitat is favorable - as long as that occurs before the OFFSPRING of your current fish reach crayfish consuming size!

Hopefully, some actual experts will drop into your thread. In my limited experience, I believe crayfish are an awesome supplemental food source! So I hope you are successful.