I'm no expert, but if I were doing another one..
The depth, I'd make at least 16 1/8 (keg dim), and I'd be thinking about a tipper for the mash & kettle.
Your going to need some more support on cross members, and a diagonal wouldn't hurt.
On the back side , there is no vertical support. On the top there is no cross support.
I'd take the center out, use angle to form "cradles" for the kegs.
I could definitely go deeper than 16", just didn't see the need to since my kegs bottom diameter was 15" (There are several different keg dimensions).
Tippers not an option for me. I considered it, just don't think it will be worth the work. I will be removing the grain via a shopvac. No lifting required.
Yah I might put another post on the back side. The one in the front is just for the march pump mount. I don't think other supports are necessary with the steel. Seems like a lot of rigs are overbuilt. I could be wrong though. Would be interested in some numbers in what is really necessary for supporting 13gallons of wort in a keg.
I considered angle iron to cradle the kegs too. I might change my mind but I don't feel the need to cradle them. Since I am using a 60qt coleman for my MLT I think it might be more of a hindrance.
Thanks for the reply, if you were to put other supports where would you put them?