Hey JackG79,
Congrats on progressing through the tech tree and getting to the Iowa. This ship can be fantastic if played correctly or it can be a nightmare. There are a few features of the Iowa that I see players use incorrectly. The first is the speed, yes it is awesome to sail around at over 30 knots in a BB but this can often get you into places too fast. What I mean by that is because the Iowa is so fast you can leave your support or find yourself over-extended very quickly. The other thing I see a lot with Iowa players is they tend to back up and not use their speed/maneuverability as an advantage. The Iowa is not designed to sit in one spot and back up. Now, that we got that out of the way let us try and help you with a build. I see some of the other captains have done a great job in outlining skills and builds.
I build the Iowa just like I do most other BBs: PT, EM, SI, CE, FP, BoS and AR. I also pick these captain skills in the same order everytime (the only place I can see a shift is the FP or CE choice).
One of the most important modules that you will access to on the Iowa and later the Montana is the Artillery Plotting Room Mod 2. . The reason why this is so important is because it gives you -11% to the maximum disperion of the main battery! Yes, it is 3mil credits but it is well worth it.
The rest of the modules are the same as other BBs that I build
Slot 1: MAM1
Slot 2: DCSM1
Slot 3: Kind of meh but go with AAM1
Slot 4: You have some choices and they are all viable imo. I tend to go with steering or the damage control but propulsion can be used. This will be a personal preference slot.
Slot 5: CSM1
Slot 6: APRM1 (You could go reload here if you want).
Hopefully this helps and enjoy the Iowa!