Just some initial comments, but I hope they start a good conversation to get you exactly where you want to be.
Looks like you've got the key switch safing the whole unit. Check.
Once you turn the key, you get an indicator saying the unit is 'live'. Check.
You have a flip up cover to prevent accidental switching of the arm switch. Check (not sure if required, but nice to have).
You have an industrial quality lighted pushbutton that indicates 'armed'. You push the button and get voltage at the outputs. Check-ish.
It would be ideal to see your schematic, even if it isn't picture perfect. That would make it easier for those smarter than me to see any possible faults.
At this stage, I'm not clear what happens if you actually burn the igniter. Specifically, do any of the lights change state or if you have an open circuit (i.e. bad igniter, already burnt igniter, clip fell off etc.) do you have any indication? I'm not sure its required, but it is a nice feature.
My biggest concern would mostly be 'what do you plan to launch?' If you're going to be flying in your own back yard on single Estes ABCDE engines, I think you've covered all the basic safety requirements that Estes controllers have. If you are going to be flying in a public park, I think the key is the key (see what I did there. . . ) to being good as well. If the controller isn't in your hands, the key better be.
If you are planning on launching clusters with this controller, it might not be ideal. A relay based launcher keeps the path to the igniters short, but the trigger far away. While the pushbutton you have might be good for 20 amps, if you run 50 feet of 18 gauge wire to the rocket, it has to pass the current 100 feet (there and back) to get voltage to the igniter. You get voltage drops along that path and things get less reliable. Bigger wire helps, but the long travel path is not ideal in general.
Personally, I built a relay launcher years ago and that's what I use when/if I fly solo. I do like clusters, so it made sense at the time.
If you want the buzzer to work, definitely post the schematic and someone can help with that.
Last comment is just personal preference, but I hate wire nuts. I am ok with crimping (with proper tools, not the $5 kit from the auto parts store) using the proper crimp sizes and wire loading. I'm ok with soldering if wire sizes and prep are logical (i.e. 2watt iron and 3/0 wire, not good). I'm ok with terminal blocks if they are properly made. The only time I use wire nuts are in home wiring projects to keep the inspectors from asking questions. Others may disagree, but that is my feeling. If you get more comments about wire connections than your project, I apologize. I might have just started the electrical version of a glue thread. . . not my intent.
Obviously, burn a few igniters in controlled settings before using it, but I imagine you already planned to do that.
Sandy.