OK, so you beat my minus 6 degree record (I did not know the temp until I got to work and someone was horrified that I had biked in that. My eyes water in the cold and my eyelashes were freezing to my glasses).

Fenders are well worth whatever the weight or cost. Only the tips of my shoes ever get a bit of spray from the edge of the fenders. I just upgraded to an oversized Marmot Precip and am very happy with the increased comfort (love those pit zips) over the second hand get-ups I had tried. I got a pair of coated nylon rain pants second hand (but new) and after one use (it finally rained here) I may spring for a breathable pair if anyone says they will actually breathe during exertion. I don't think any modifications I had planned will make much of a difference in the coated pants.

I have a Bell Metropolis helmet with rain shield that I like, but the hood on the precip is large enough to go over the helmet. The rain shield stays on for the season once I put it on, since it is difficult to get on, and it makes the helmet hotter than I like in nonrainy spring and fall temps.