I don't have much to say regarding making framing chisels, but I do use them every day, both new and old.
The tool steel plate on my antique chisels are a little more than an 1/8" thick, probably more like 3/16" or a hair more and and roughly 3/4 the length of the blade. 1/4" sound to thin for the blade as well, maybe tapering down to 1/4" before the bevel at the cutting edge, you might also want to consider a central ridge so that the chisel blade has a nearly triangular cross section but roughly 1/8" at the edges, this makes it much easier to remove it when it's jammed.
I would also strongly recommend a socket handle, more time forging, but much easier to rehandle and much less likely to break the handle.
Just my 2 cents, let me know if you want me to take some pics and actual measurements.