#1. I would maybe invest in a larger box... 12 x 12 gets really small, really quick.
#2. You dont NEED the SS compression fittings for the BCS probes if you dont WANT them. The probe comes with a compression fitting already, if you want SS, you have the right ones spec'd
#3. You may want to include fuses for your pumps, BCS and maybe elements. Your breaker will trip at 50A, which is about 10x what you need to fry most of those components before it trips.
#4. How are you getting the wires into the box to the SSRs? You should probably include some liquid tight cord grips from a place like ElecDirect. Otherwise having a NEMA 4 box is really a moot point if you dont have water tight connections.
#5. Id look into using 3/4" plumbing on 3/4" SS Camlocks from ProFlowDynamics. You will have to get an adapter to fit them to the pumps and valves, but this would reduce your resistance and increase flow on those March 809's.
#6. If you are going to use the SS coil in the HLT mounted to weldless bulkheads, you will need some 1/2" SS 90 degree elbows to get from the coil to the female end of the weldless fitting.
#7. A range OR dryer cord will work for you as long as it is 4 wires and rated to 50A.
#8. How are you powering the BCS? It comes with a wall wort, so you need an AC plug to plug it into. I get around this by having an outlet actually wired up INSIDE my control box in a smaller box so that I can literally plug it in. You cannot just touch the wires to your terminal block. BOOM.
#9. Wireless capability... dont bother unless you have the utmost rocking high speed connection available. There is SO much data transfer that you will have real continuity problems if you are not connected via a CAT6 cable or the like.
#10. IF you decide to place a fan on the control box, I would recommend 100CFM or greater of you really want to move air... you will also need to cut some intake ports, otherwise there will be no air movement. Even with intake ports you will be cutting some of the fans eff. so I would get a nice large fan 105 CFM or so.
#11. You are going to need to get some M3 (if I recall) screws to mount the SSRs to the heat-sinks.
#12. Tube of heat grease from Radio Shack
#13. I, personally, would place (2) SSRs on each element. This way when the BCS commands it off, there is no current to it. Otherwise your rig, just plugged in, nothing running, will have current running to all of the elements. Just my .02.
#14. Where are the SSRs for the pumps? Are those the 25A ones? Typo?
#15. You need some SS 1" couplings OR 1" SS nuts to mount your elements in your kettles.
#15. You need the misc. pieces to pot the electrical connections on the elements.
#16 Get some 22ga wire to run for the BCS grounds and such that run to your SSRs.
#17. You have 2 terminal blocks spec'd. but you will have 4 wires coming into your box, how will those be configured? Personally, Id go to Automation Direct and pick up a 3IN 6OUT distribution block and then have an additional terminal block or ground bar for the grounds. You will need a place to split (2) hots, (1) neutral and (1) ground
#18. Also, as I said in my PM... Id go with a RIMS. If you are rockin 9000W in the kettles anyhow, Id place that in a RIMS. Use that RIMS to heat your strike water right in the MLT, use it at 4500W for the MASH and then use it at 9000W for on demand sparge water heating. It is a more eff. use of energy overall. It will provide you with plenty of hot sparge water I assure you.
These are the things I see off the top of my head... arent you hating that you asked for my input now?
Really there are a lot of things you dont think about until you are mid build... or on your second or third build. It is a process.
When building something for the first time, I take the "proposed cost" and increase it by about 30%.