If your house stays around 78 ambient, you really don't need both a heating pad and a CHE. If you want to keep a thick layer of substrate, then the CHE is probably your best choice for creating a warm spot. If you want to lay down paper or a thin layer of aspen, then a heating pad is best. They only need the substrate to absorb waste...it's not a "comfort thing" for them...except that sometimes they really enjoy hiding under paper.
ANYhow...
If you have a unit that has two probes...then just place the probes as you say, and mount the unit on the outside of the enclosure. For most of them, though, the unit itself is the "probe" for the cool-side temps and humidity. In that case....run the probe under the substrate to the warm side...and simply place the unit in a corner of the cool side of the tank. I just lean mine up against the side, facing out. Yeah, they can knock it down, so sometimes you have to pick it up to look at it...but that's much safer than risking them getting tangled in tape or other mounting sticky stuff. (And I have had one peed on so copiously that it shorted out and had to be replaced...LOL...but still, worth the risk of a tape-free environment)
Hard to say without actually seeing the room and set-up. Can the tank be kept away from the direct blow of the fan? Is it a ceiling fan? Moderate air circulation won't hurt at all...but a hard blowing fan directly on the enclosure may make it difficult to keep temps and/or humidity steady. You might be able to counter this by simply draping a towel or something across the top of the screen.
She's a beauty!! Welcome to BP.net!

I hope you stick around after you get her!