Thinking of making a wiz/cleric build. With Wizard as my main class.

Why? Because when choosing the 1st level of the other one I will gain more spell points than regular pure leveling.

What I don't know is:
what level of wizard do you gain level 9 spells at?

if I multiclass from wiz to cleric do I lose my wiz spells? and same when I go back to wiz from cleric will I lose my cleric ones?

Tks