How many electrons are total in the levels of a stable atom?

Well it depends upon which element you are talking about

Eg flourine atom has 9 protons and electrons normally configuration will be 2,8,1

But if u r talking about a stable fluorine electron, configuration will be 2,8

This happens since the outermost octate of fluorine is not filled completely so it is not stable in it's structure so it loses the 1 extra electron in it's last octate and becomes stable gaining a negative charge

Ultimately no. Of levels vary from element to element