The model setup itself is fairly easy, although it's been about 10 years since I last used Arena. Your biggest challenge to start is tracking box arrival/departure rates for all of the points. You need to determine the time distributions of these to see if they fit a standard distribution or if you have something else going on. For instance, boxes arrive based on some sort of normal curve but conveyor errors cause blips in the system. That's a start. Obviously if you have a high number of SKUs this model could become complex very quickly. If you're running a system with a lower number of SKUs it's less complex.
Arena will allow you to add conveyors, time distributions for conveyors as well as VA points, plus allows you to model in sub-routines to cover downtime occurrences.
The biggest thing I will tell you from past experience is that once you have a model developed and it has run into a steady-state output range, you need to validate it against your current system. If you're dramatically off, you end up going back to your model to see where issues might be occurring. I won't state that simulation won't help you, but you may find some other options exist for identifying and tracking bottlenecks without going to the efforts of developing an accurate simulation model. It all depends on how complex or simple the system is. My experience with distribution centers to date is that they usually feature a very high number of SKUs and model development is very time consuming.
