If you want to substitute an real actress, nothing will be "forgiven". You may not need an AAA performance, but at least everything has to be believable - and getting small hand movement believable, subtle changes in balance too, walking, running, standing - if you want to do that believable, you will need a really good animator, and loads of time. If the body does not do subtle movements to support the expression in the face, then most people will see through it instantly.

A ship in port is safe; but that is not what ships are built for.
Sail out to sea and do new things.
-"Amazing Grace" Hopper

Avatar image of me done by Chidori.