RE: to much washout?
What's too much washout?
Almost any at all on a non-tapered planform. Any at all on a symmetrical wing if you plan to fly it "symmetrically".
And you need to consider what the wing already has in it. It might have aerodynamic washout. And if it's airfoils differ from root to tip. And how much it's tapered. The question is way too general.
But if you want a soundbyte answer..... More that 2degrees is usually a waste and actually detrimental aerodynamically. A couple of degrees is almost always enough (when washout is appropriate and needed) to reduce or eliminate tip stalling. And when it's not, our having done the washing out convinces us that it is. And if we think something is helping, whether or not it does, it does.