1) marginal differences in what hoops need to be jumped through before the aggressions of the state (technically just other people calling themselves "the state") is percieved as legitimate. in a democracy, the potential tyrant needs only to point to a popular vote. In a republic, tyranny is somewhat more difficult to pull off, but obviously still possible... if a potential tyrant needs a majority of senators or congresscritters in lieu of a majority of general population before he can rob you, it is harder for him, but obviously not impossible
2) There are marginal differences, with a republic being marginally more difficult to institute oppression (as mentioned above), however the tradeoff is that such oppression is cloaked in more of a veil of legitimacy. If youre robbed by some asshole who says that "the majority" authorizxed him to, you might see through this insanity very quickly "Dude... wtf does the majority's say have to do with your right to rob me".
HOWEVER, if youre robbed by this same asshole who now points to a magical parchment signed by people you never met, supported by some men in robes and some other men in a big room, you may balk at protesting your oppression for fear of angering the magic powers of the old parchment or something silly. "Oh, so that magical parchment is why im not raped on a daily basis, why gravity exists, why theres air in the universe, etc... and youre suuuuure your right to rob me is authorized by it somehow? I dont wanna anger it. Ok, here's my wallet"