Having 4 wives is mandated or just an ideal number but you can still have more if you want?
It's mandated to have no more than 4 wives.
two or three or four
These are the words of Allah and therefore may not be argued.
If it says that you can only marry up to four women then why heard cases of marrying to 7 up 10 wives?
Just like with any religion, there are cheaters and sinners. Some of them are inventing alternate reality constructs in their mind, trying to fool themselves, while others are not even bothering this and just doing whatever they want.