Damned if i know wrote...
3/16 and especially 1/4 are far too thick.

Not in my opinion. I have made plane irons from 1/16" to 1/4" thick for a
wide variety of planes ranging from block planes to jacks, and infills
including shoulder and chariot planes, as well as dovetail and rabbetting
planes. In almost every case, a thicker iron offers superior performance.
(There are exceptions.) A notable drawback of thicker irons is that
honing time is generally increased, but this often can be countered by
using micro-bevels.

you may want to consider not tempering
back. You'll have a blade that will hold an increadible edge and be also
harder than any chisel or plane blade you have now. The blades I've made
that I have not tempered back don't show any sign of a chipping problem.

This can be true, especially if the steel doesn't attain its maximum
hardness at quench. This is because it is nearly impossible to
consistently achieve initial hardness higher than HRC 62 in O1 without
tightly controlled temperature, I.e., a heat treat furnace. If you can
hold the temperature between 1470 F and 1520 F for a 20 to 30 minute
soak, and quench properly, you can get quenched hardness of HRC 64-65
from O1 all day long. *Then* you need to temper back to 61 or 62 for a
good woodworking edge tool. If your as-quenched hardness is running in
the 61-62 range -- not unusual for forge-hardened blades -- you get less
(but still some) benefit from tempering.

To avoid warping make sure the oil you use for quenching is quite hot to the
touch.

Good advice, and often neglected. 120-140 F is about right. A candy
thermometer comes in handy for this. If you have a small volume of oil,
it will heat significantly during the quench. If you're doing multiple
tools, wait between them long enough to allow the quench to cool back
into range.

Another thing to help reduce warping, cause its a plane blade there
is no need to harden any more than the first 1 1/2

Also, warping is often more pronounced in thinner sections. Additionally,
the presence of a bevel causes some warp. The quenching technique
contributes, too.

You can take advantage of the latter to counteract the former. In
general, edge tools tend to warp so as to crown the bevel. That is, the
surface opposite the bevel will be concave. OTOH, the first portion of
the steel to hit the quench "shrinks", forming a concavity there.
Consequently, you can start the quench at the bevel in order to
counteract it's tendency to crown.

It takes some experimentation to determine the best angle at which the
tool should enter the quenchant, as well as the best agitation motion for
the tool while in the quench. Sometimes it's better to plunge with the
tool pointing straight down and then move it in the direction of the
bevel. Sometimes it's better to plunge the tool straight down, but held
at an angle so the the bevel hits the quenchant first, and then move the
tool straight up and down in the quenchant.

You can reduce the amount of warping in a thin blade by clamping the tool
between two thicker pieces of flat steel, and heat treating the whole
unit.

Cheers!

Jim