The wood racks will stop seeping, mine did by the time we had the 2nd smoke, I draped a little foil over them to keep it off of the meat while it was coming out.
You might look into lining your heat chamber where the burner is with some duroc cement board, it works well in protecting the plywood. Or even tiling the area, I have seen a few like that.
I kept my temps around 250, I did have a burnout, but that was because I was trying to center my heat and put that aluminum box around my charcoal, forgot to burn off the paint first. Was in a hurry, getting in a hurry can be an issue lol. Learn from my mistake.
Almost done with my repairs, been busy at work, so haven't been able to do a lot with it.
I like the rack system, but you will find that even at 200 degrees the wood glue won't hold up long, screws are definitely the way to go, its not as 'pretty' but I cut some thin strips of wood and used a brad nailer to cover them up, can't notice them, and it looks like some extra trim.
Your heat shield may be a bit much with that burner, I dunno, I ended up just sitting two disposable aluminum pans across my lower rack to catch the drippings, got them at the dollar store, also got some of the little wire racks they sell there to place under them for some extra support. Remember with the wood, you really don't want any item retaining a huge amount of heat, it will eventually give you what I had with the burnout. While the cook chamber might not be more than 300 degrees I would bet that piece of solid metal above the burner is a lot hotter.
I definitely defer to the guys with more experience, just passing on a few things I learned with my build.