the use of azelaic acid

Azelaic acid has no conflict with niacinamide and retinol. So yes you can use this along side them. Its often used by derms compounded with tret. It can also be used AM and PM no issue. As for side effect, Like any medication it can some reaction or side effect. More notable is itchiness ( for me anyway) but mine usually last 10 secs and its normal. I would suggest maybe using all your products separately first observing how your skin tolerates and slowly layer them together after.