Is the Gen 1 brake-by-wire like the Gen 2?

All Prius generations can be described as kind of brake-by-wirey, but the 2nd gen was distinctly more brake-by-wirey than the ones both before and since. You can pick up some of the reasons from this post.

As your particular interest is in the differences between Gen 1 and Gen 2, the New Car Features manual from 2004 (more info) is what will answer most of those questions. Proportioning of brake force front-to-rear was done with a traditional proportioning valve in Gen 1, and they folded that into the electronic control for Gen 2 and called it EBD (electronic brake-force distribution). They also managed to eliminate the little sliver of always-friction down the Gen 1 side of this illustration, and use pure regen in that area.



There's more about that in this post. That illustration, naturally, is from the 2004 NCF manual, already mentioned.

 

Probably more accurate to chalk that difference up to the ECB function in the Gen 2.

I didn't put an exhaustive list of the differences between the gens into the post above, just a few to get started. I linked to a couple other posts where there's a bit more, but those details all come from the New Car Features manual already mentioned.

If the design differences interest you, and it sounds like they do, you'll eventually want to just read about both systems, meaning pages 100 to 121 in the 2001 NCF, and pages CH-29 to CH-72 in the 2004 NCF.