Hey, I've been down this road before
I freaked out a bit at first, but after replacing a fuse or two things were back up and running.
My bus has the T444e, which is the same block as the Powerstroke 7.3l, but I can't promise that the wiring is anything similar. On my bus there are two fuses in sealed fuse holders directly connected to the main positive lead right at the battery. Check those out. Then go through the fuse box inside the vehicle (or under the hood, wherever it is) and test all of the fuses that control the ECM, the VPM and the IDM.
After fixing those I was up and running.
In the future, if you need to disconnect the battery you may be better off removing only one of the leads. That'll make it damn near impossible to reconnect the leads backwards.
I hope all things go well!
Oh, one more thing: if you suspect that the glow plugs aren't lighting then it's probably the glow plug relay, not the plugs themselves. When my relay died on me a couple winters ago I would jump the relay terminals with a screw driver for 15-20 seconds before turning the motor over. Worked like a champ.