I would totally suggest an IAC. Im just down the freeway from you in Aberdeen. You have a powerful ecu, I would use it to its full advantage. MS3 has idle correction, idle air correction in closed loop and when its working together it just like stock ecu. You can use an initial value lookup table to catch the idle then have it drop just like factory. Im running S1's with a manual car, I command an 800rpm idle at temp, and in all conditions I can see the iac/timing working together to maintain my target idle.
Mornings like today where its 21* its nice to have a 1300rpm start up idle and have it ramp down as it warms up.
Not having one is fine and works all the time, but with a little knowledge and some trial and error, you can have such a better idle control/quality.
I found running the Ford PWM style works better than the stepper, and I would be willing to make an adapter for you. I have the Pro on my 2j, and just picked up an MS2 kit for a 22re im working on, the one has, the truck will get the pwm idle motor.
Agreed on boost settings. Let me suggest another route. Set your WG pressure to your desired rainy day boost level. Have the switch on the dash control the 12v power to the solenoid. In effect you can get 3 settings. Granted I have a $hit ton of power, Im using gear based open loop table switching, so I command like 12psi in first, then ramp into my secondary table where I get 18 in second, then 24/25 in third. So if you can get a vss input installed and setup the gear page, you could also do boost by gear in closed loop boost.
On a side note, once you get it all setup, I am running fuel table swichting based on RPM (at 3000). I have the rpm/kpa values setup that I have a 26x31 VE table. The car drives so much more smoother than the 16x16 table. My VE1 is ramped up to 6psi and 3000 rpm, so there is lots of resolution, then at 3k it switches to VE2 were I have like 3 vacuum bins, but have boost resolutioned out in 20kpa increments up to 35psi. As soon as I made the switch and let VEAL do the its work, drivabilty, especially off ide was greatly improved.
You have a nice build, following along.