Even with the highest resolution blueprints I usually have to switch to high quality rendering to get decent detail when I zoom in, and then Xray mode doesn't work, so don't worry too much about that, Maya already has it's problems on that front.

As for using photos as blueprints, you'll need to take them from a dead on angle to avoid it causing too many problems, and don't rely too much on them since they'll be perspective and blueprints are normally orthographic views.

What are the vehicles you'll be modeling?