If you just want to fire a set of task notifications on every tick, it might be simpler to use the TickHook function instead of a timer. This function will run inside the tick ISR, and thus would use the FromISR versions of the notification, but also drops a lot of the overhead for switching to the timer task and running the call back.
Timer Callbacks are better for slower operations.
One thing that I would suggest, is make sure you started with a good foundation description based on requirements, not implementation ideas.
What things need to be done when (Don’t think of tasks yet).
What things are time critical, and how critical, and what things aren’t.
What things depend on what other things.
What things do we need to wait for or store up (these become the Queues, Semaphores and the like)
Then you can look at partitioning into Tasks and assigning priorites.
There are multiple ways to do many things, and even at times multiple reasonable ways to do things, and until you see a problem, it may not be worth worrying about finding ‘the best’ method.
Your original idea of doing these operations in the timer isn’t wrong at the simplest level, it just didn’t meet your requirements of priorities of actions, and if you had fully gone through this sort of design process, you should have seen that you wanted the 1ms period operation to have priority over the slower operation, and the fact that you couldn’t assign priority to the timer callbacks could have been a hint to the issue.
This goes back to your question of which is the better way to fire the notifications. There are a number of ways to do it, the timer task method ‘works’ but has more overhead. The tick callback has less overhead, but adds some new API to learn. To use other hardware timers perhaps gives you more flexibility, but ands more systems you need to understand. Tradeoffs. If everything is, and will be, multiples of your timer. tick, then I would use the tick hook, as it isn’t that complicated to use, as long as you understand how to do code within an ISR.