Is it from the Sunnah to consistently recite all the morning and evening adhkar and those before sleep, or is that exaggeration and excess, and is it better to limit oneself to some of them?

A Muslim should consistently recite the prescribed remembrances (adhkar ma'thura) to attain their immense reward. This is not extremism, but rather a sunnah (definition) (prophetic tradition). Whoever is able to recite all of them will receive a great reward, and whoever is unable should limit themselves to what they can manage. If one adds unrestricted remembrance (dhikr mutlaq) to the prescribed remembrances, it would be even better for them, as Allah has commanded us to remember Him frequently and has praised those who remember Him in all circumstances.