Alamo,
The pickup I fitted is about 1cm thick, so it is not that thin. However unlike a lot of lower priced resos, my Busker has a nice steep neck angle, which not only gives a good string break angle over the biscuit bridge and the ability to really dig in with your playing, but also means that the strings are quite high off the front of the body. Not high enough to fit the pickup to the fretboard end but, in the location I have put it it gives well enough clearance.
There are two other pickups that may suit. One is the FlatBucker, which is made in Germany , the other is the Lace Sensor.
Try this link
http://www.buskerguitars.co.uk/shop/...YZ&shop_param=
Also Kent Armstrong do something called a SlimBucker.
Dont know much about harmonic nodes for pickup placement, I simply put it in the best place for what I wanted to achieve with it, which was amplification, yet ability to return the guitar to its original state.
I looked into making my own hotplate, but the National one is specially designed coverplate, with a pickup slot where a set of soundhole would normally be. Also dont forget that any pickup you put into a hotplate cant be too deep, as it could get in the way of the cone. It will also be at a slight angle unless you can get a fairly flat coverplate.
One thought I had for a hotplate idea, was to use a tele bridge pickup instead of a tele neck one. Then you have three point adjustment and probably better tone as well. Just my opinion.