The things you listed above would make him completely broken.
Garen would become a monster with: a ton of health (Build) + high regeneration rate (P) + high armor (Build)+ a silence (Q) + movement speed boost (Q) + slow remover (Q) + a stun (Q)+ a HUGE amount of tenacity (W) + a TON of % damage reduction (W) + a shield on top of all this (W) + an AoE fear (E) + EVEN MORE DAMAGE ON HIS ULTIMATE (R).
Essentially he would become an extremely tanky, high damage champion with so much resistance to everything including CC that he would basically be able to 1 v 5 late game just by flashing into a clump and pressing E which would apply a fear to everyone surrounding him and if that wasn't enough, he would gain a shield on top of the % damage reduction already gained from the normal W AND if even this was too small for you, he has the ability to STUN now. His silence is already annoying but now that silence can STUN. To put a cherry on top of the already so sweet cake, his ultimate does even MORE damage on top of the high damage it already does against low health champions AND the true damage it deals against villains. To put another cherry on top of the cherry which is on top of the already so sweet cake, his laning phase will be broken. His passive already healed loads but now its doubled. So basically he can go in, stun+silence someone, deal damage with E while applying a fear (all this CC would leave the enemy helpless but to just stand there and take it) and after all that just walk out while taking little to no damage because of his W which would give him a shield on top of % damage reduction and tenacity. If he does somehow take some hits, he can sit under tower, think about life while his health just springs back up and go rinse and repeat.
Are you sure you've thought this through? Because when listed out like this, Garen instantly becomes a god. Think about your proposal a little bit more because I don't even play Garen a lot and this kind of buff already sounds insane.