The minimum effective routine is cleanser, moisturiser, and SPF. Everything else is added based on a specific concern with one active ingredient introduced at a time over four to six weeks so you can see whether it makes a difference.
Skin purging is real. Retinoids and acids can cause temporary increased breakouts in the first four to six weeks as cell turnover speeds up. This is different from a true allergic reaction which involves widespread redness and itching. Knowing this distinction prevents abandoning a product that would eventually help.