Yes, you must clear security at the SFO International terminal. There is no airside transfer available from any terminal. QF feeds you quickly after takeoff (about an hour), plus there are some sandwiches and biscuits in the SFO lounge, so probably best to eat at DFW terminal D (the Irish pub there seems to have the best food amongst the various cafes). But you do get food on AA in F as well (probably on both sectors), which is a lot of food with little exercise. I always find with 3 connecting flights it is too much food in aggregate rather than too little, but to each their own.
As for the showerheads in the former FL at DFW, they are rather easily obtainable everywhere in the US for circa USD 50 -- quite a bargain. Often sold as Australian Rainshower or Rainforest showerheads, though there are many brands (all identical from what I can see). And yes, it is a mandatory home renovation from my viewpoint.