I've been working the past several months with Mitsubishi PLCs, and have done several projects like this one. My regular choice when developing applications similar to yours would be FX3U/3G but I have also done work with the FX1S/FX1N. Being an older generation of PLCs they are simpler to use but provide fewer functions.
As far as the HMI goes, I haven't used DAQFactory before since i normally use Mitsubishy HMIs for which I design the layouts in GT Designer / E-Designer (both Mitsubishi specific software)
but I assure you that this is not a problem, I've checked it out and DAQFactory doesn't seem all that different.
If this doesn't assure you that i am up for the task and my 200$ fee is worth it, i would like to mention that i've already done a project much alike this one where all the factory's waste water was treated. The system was a FX3G - E1020 HMI and manages 10 tanks, the biggest being more that 10 cubic meters. The task was to transfer the water being collected in 2 collecting tanks (one containing heavy metals and the other just having bad Ph) to 2 corresponding neutralizing tanks where by opening 3 electrovalves (acid , oxide, base) it changes it's alkalinity to a specified value. The system was quite complex. If you are interested i can provide samples of the HMI, the Ladder Diagram and the Electrical Schematics.
Looking forward to hearing from you,
Valentin Manu
Automation Engineer