Laravel how much or how many things should a queue process

It will depend on race conditions.

In the chain, is step 3 dependent on what happened in 2? Is step 4 dependent on 3? etc.

If they need to run in order, then you should use only 1 queue or even from within the same Job.

If it really doesn't matter, then you could use multiple queues, but it's not needed, having 1 queue and 4 workers it would behave in the same way.

@lostdreamer_nl no they are not dependent on each other. I mostly wonder if it has any performance impact or any other pros cons beside that I can more easily check witch job failed if I keep them in seperated queues

"is there any best practise regarding queues on how much a queue should process"

No, a queue is build to not really care about 'how much is in the queue'

The only thing you have to care about is how much heavy jobs are being processed at the same time (so having multiple queues doing heavy things would need more coding on your end to make sure the server has enough resources)

For now: simply go with 1 queue and put everything in there.

Sending the emails and notifications are likely to be the slowest processes. If you need the Model 1, 2 and 3 updates to be nearly instantaneous I would either code them inline or place them in a separate queue. It's relatively easy to determine timing and workloads when a single user is accessing your site but if you had many concurrent users your queues could have a significant number of lined up requests.