How many bounced email addresses are normal?

That really depends on the condition of your list.  If you have been keeping things current and stayed in touch with people via email, then the bounce rate should be low. However, your first campaign might see bounce rates as high as 20%. Don’t be alarmed if this happens because it will like improve over time. There are some things outside of your control. Corporations change there filtering standards all the time. You might have to request that people put you on their white list so you don’t get filtered out.