I recommend starting small with a single main agent using a reasoning model and tools.
In the prompt add a "process" section which clearly states the steps it should take (step 1: orchestrate, step 2: review productboard etc...)
For the custom instructions, add them in the main prompt.
=> I got pretty good results with it and it allowed me to iterate fast.
Once you have a good understanding of your challenges, you can go the specialised agent root.