I got to spend a couple more hours on it and I'm just about finished with my first prototype. I still have to add the circuitry for overload detection and lockout. That didn't stop me from testing what I have completed so far. I get in a hurry like that sometimes. ;-)
After verifying that things looked reasonable, I hooked it up to a piece of test track and lo and behold it worked beautifully. :-) I ran my DCC converted Athearn back and forth at slow speeds. I also was able to turn the headlight on and off. I haven't tried programming yet, but I see no reason for it to not work.
As it sits right now, the circuit with PIC, LCD display and h-bridge operating draws just under 20mA, not counting anything on the track of course. I expected it to be higher since the h-bridge datasheet specs it as using ~15mA quiescent current by itself.
Too small for me, I have to check every solder joint with a loupe as it is. I don't relish the idea of working with parts that can be accidentally inhaled. ;-) That goes for locomotive decoders anyway. I plan to try my hand at trackside accessory decoders though.