John, #1 you should be having this discussion with your local Juniper partner and/or Juniper account team. As far as attenuation is concerned, as long as received signal is within specs no attenuation should be needed. I would expect over distance this should not be a concern. Also for any standards based optic from any vendor the transmit hotness should also be within spec so that no attenuator is needed.
Not sure which exact Juniper EX (I assume) product you are using but VC across a WAN is fully supported. Officially needs to have less 100 msec roundtrip delay. Also generally VCP (VC over Ethernet) is spec'd to be at 10GE, although 1GE often works. This is an area you should discuss with local folks before you implement.
Not sure how helpful this is to you, but good luck. I'd start with #1 above if I was in your shoes.