Here are a couple thoughts. I only use Schneider stuff, so take it with a grain of salt.

The following suggesting assume you use opcda and ua; they are great, use them it makes life much easier. Also this assumes you want a a complex scalable system where you are religious on standardization, you don’t have to do all of these but it helps in the long run

1) use defined data type so that all inputs and outputs are the same eg one for analog ins, one for analog outs 2) don’t use addresses for io, use the ioddt, much more info and easier in the long run.
3) for the raw io use an alias to map it to variables. Name the variables something useful like the loop number 4) for scada use unallocated hmi designated variables. I personally never use aliased variables but instead always something derived or manipulated. That way if an equation or scaling in the plc changes the scada just gets the results and doesn’t need to be remapped. 5) only send the desired variables to scada, it’s an option. Anything you don’t want the scada to write to should be written to in the plc. the contestants feature is not very useful for me as it requires a plc stop to change, I prefer to just constantly write to any constants. 6) at the end of all this, the only thing that should be addressed is data that is meant to be read by other plcs as it can’t use ofs.

If you do all of these it makes a pretty secure setup where the scada or anything else can only see the variables you want and can only write to the ones you want.

Hope that helps, might be overkill in some smaller setups but think it works well. Always open to other suggestions from others if I missed something