Good luck with this project, I am in a similar situation, difference is I'm replacing the fuel tank. While the subframe is out, I will also be replacing all bushings. What started all this was constantly getting minor fuel leak code (forgot the exact code). What I originally thought was a corroded fuel fill neck turned out to be broken barb nipple coming off the fuel tank.
I don't want to further hijack your thread and let me get to the point of responding to your thread.
This is only a suggestion but there is no need to weld a plate to reinforce the rear sway bar bracket, I used straight strut bracket. You can buy this at Lowes or Homedepot. The bracket is only bolted on through the top hole with a big washer as the hole that is there is too big for only a nut and bolt. I've also only drilled one other hole to line up with the sway bar bracket