One thing my trainer, Alexandre, always told me to do that helped me a ton during my radar training, is putting everyone on the same downwind, which in most cases would be the safest downwind out of them all.
This will help a lot with organising your airspace and with not also having to think about when to turn them so they don’t make a conflict. This technique is mainly used at a one runway airport.
However, for a parallel runway airport, I suggest using one downwind for only Radar Vectors, Visual approach, and the other one mainly for GPS and ILS approach to help organizing things as well.
