As Salam mualaikum brothers and sisters. Remember this very easy saying. Islam is very easy, it is people that make it difficult. The prophet was flexible with many things that in some cultures have become strict. Remember it is the intention of the believer that is most important and the actions then that follow, and Allah knows best.
The prophet would at some nights be up all night praying, maybe praying more than 20 rakahs but this is not obligatory prayers so therefore we are not answerable for them on the day of judgement. What is important is that we complete our compulsory prayers and offer the sunnah prayers after.
With regards to Umar prescribing 20 rakahs for the night prayers during Ramadan (which we call taraweh), it was to unify the Muslim ummah and prevent fitna and disobedience. We are all one in the eyes of Allah, and Muslims argue over the minuscule of subjects while neglecting their obligatory duties.
This is a matter of fiqh, just like people praying in different manners. The prophet tried to teach us that it was the worship of one true God that was important and it can be done in different ways. The madhabs were then created because of the discords and disunity between the
Muslim ummah. It is better that we have a united front instead of the segregation we see today. It is not a matter of Aqeedah, therefore should not be a matter of debate amongst the populous.
However, it is always good to question and seek the answers truthfully without prejudice. It is encouraged to increase our intellect and understanding of our deen.
May Allah guide us all along the siratun mustaqeen - the straight middle path of no extremes