I'm going to be starting my second knife soon, a broken back seax. The first knife that I made was a seax style as well, but I more or less did not care about accuracy so I gave it a full tang and dimensions I thought were visually pleasing.

I'm hoping to make this next one as historically accurate as possible. The dimensions I have planned so far are:
Blade length: 7 in
Blade Width: 1.5 in at the peak of the "broken back", tapering down to 1.25 in at the tang. The broken back peaks 2.25 in back from the point.
The tang will be 2.5 in long by 0.75 in wide, a rounded rectangular shape.

The tang seems a bit small to me but it doesn't seem far off from many originals. Also the stock I have is only 4mm which I think might be too thin for a knife of this size, what are your thoughts?

The other questions I have concern the construction of the grip and the bevels. I'm going to build a simple jig for grinding the bevels now, but I'm not decided on the angle and I'm not sure of the historical norm. The push tang quite frankly scares me. :p I'm guessing that the right way to go about it is to carve scales with a tight friction fit, and then epoxying the hell out of the tang before insertion... if there's any makers here that build seaxes in the historical way then I'd love to hear their input.

Thanks.

4mm is a bit on the thin side, even small handseax often have blades 6-9mm thick, but I would be willing to bet that 4mm is not outside the historical range. Somewhere around 20-30 degrees would be pretty normal for the edge on a small seax (or a larger one for that matter.) I have hafted a number of knives in the traditional manner, and a whittle tang driven into a wooden handle can be surprisingly strong, even without any adhesives. In my experience, It takes a great deal of abuse to destroy a well-made whittle tang knife, and then it is usually the wood grip that splinters and splits rather than the blade just falling out. Glueing a thin leather covering to the grip is both historically accurate and makes the grip much more durable. Antler handles are the most durable of all, I have done bunches of knives for everyday use and abuse that are simply driven into the spongy center of the antler (either dry or soaked in water to soften) and have not had one fail yet. You may want a slightly longer tang than 2.5 inches on a 7 inch blade though. 3.5-4.5 inches would be good. Remember that broken-back seax often have grips as long as the blade. I have also mounted blades in antler handles by drilling out an oversize tang-hole and just driving in wooden wedges to fix the blade and even this ridiculously easy method holds up well.