"Nepotřebujete to i říkat" can this be said?
No. You need 'ani' in negative sentences.
That's clear enough. Thanks!
"Nepotřebujete ani to říkat!" was given as a mistake, does it just need to be edited?
No, this word order is not natural and probably not correct. I guess it's because the "ani" (even) connects to "říkat" and not "to".
What is the difference between "řikát" and "řict"?
imperfective vs. perfective, good dictionaries should contain this information
Is the imperfective the more common form of this verb?
No, it really depends on the meaning. Both forms are common. On řekl. On říkal. You will meet both.