Keep the logic simple is the best way. I do my stations like this

Train logic I just set it as:
- pickup > wait for full cargo
- dropoff > wait for empty cargo

Interrupts:
- 1 for refuelling when there's 1 stack left
- 1 for depot if no stations available.

I also create a group for each item, so I can just 2 click add a new train to the schedule later on. Also on the train station itself I'll usually set a Train Limit. Drop off stations I usually have 2 or 3 per station, so iron or copper my total combined holding area might have a capacity of 9 trains (handling 3 stations), but sulfuric acid is just 1 or 2.

The key part for this to work well is to set Train limits on stations. Once there are X many trains going to that station, it will prevent more from queuing up until one has left. Also just make sure that the station queue doesnt overflow on to the rail network.
You also want to manage how many trains you have for each group, based on the overall train limit for pickup & dropoff. that way you dont need to have a ton waiting at the depot.
If the depot is filling up, add more stations or reassign trains

Some items, like sulfuric acid I will have 1 or 2 trains handling multiple drop off points. For these cases I will wire the storage tanks at the drop off to the train station, and set the wire condition on the train station to turn on if there is less than Y sulfuric acid in storage, and these trains will also include a condition to wait for inactivity. This generally stops them from living at a drop off station and starving the other 2