Personally in your AOI I would have a visible ER bit and a UDT for all the Error information - that would reduce the clutter
+1 for daba hiding initialization stuff eg EUMax, EUMin, RawMin, RawMax
If I want that visible in the Ladder I use the AOI_Tag.EuMin in the rung before
Then you will be adding instructions to the code which increases the scan time. If you do want them visible, then visibility inside the AOI instruction is the best place for them, the execution time of the AOI is not affected by having parameters "Visible".
It is worth noting that the Logix5000 platforms were designed to provide high performance, and having the processor execute unnecessary instructions every scan undermines that ethos. One day you will need that little bit "extra" performance in an application, so it is a good habit to think about it now.
Also, the good thing about having parameters that are essential to the operation of the AOI in the instruction box, is that it positively forces you to enter values when you program a new instance call of the AOI. This is something you may forget when you add a new instance after some time has elapsed. Also it is good for anyone else who has to add an instance call - they may not know about the semi-hidden initialisation code.
An example - suppose I had an AOI for valves.
Required parameters would be the Valve tag itself, the type (N/O or N/C), the I/O references (output and feedbacks), etc.
I would not include the opening and closing watchdog times as required or visible parameters, but I would add a default value (say 5 secs), to the parameters. Each and every time a new instance call of the AOI is made, it will automatically use the default value, and that value would probably be satisfactory for most of my valves. On commissioning, I could add initialisation code to move other values if a valve needs it, but I wouldn't bother with any other valve.
Doing it in this way, I am assured that each new instance call will receive at least default parameters if it doesn't require me to specify one in the AOI box.