What are the parameters should we consider in production planning of assembly lines?

You need to know the overall production strategy, is it demand based (pull) or operation in full capacity, after that, you will know final output number, availability of production lines, and WIP buffers needed, which determines the output of each assembly line.

After this high level planning, you need to get into the details of people operating each machine (their skills and availability), probably would tackle shifts if in mass production, raw materials needed, and tools required (if not fully automated lines).

Production Planning of assembly line would essentially following parameters known.

1.Annual targets.(Supplies to made )

2.Designed Production Capacity

3.Optimum Production Capacity

4.Budget

5.Supply Schedule

6.Operations Layout

7.Procurement Planning Schedule of materials,equipment.

These factors are important for production planning department to develop planning strategy of a production assembly line.In addition  liaison with production department,inventory and stores department is very important.Most essential is JIT approach to avoid any hold up of production.