Let's say I decided to start an online company called ABC Media (not the real name) with a bunch of entertaining websites under it. I registered ABC Media as a LLC. I even got a trademark (logo) and copyright (slogan) for it. Will I need to get a trademark/copyright for every website that is underneath ABC Media LLC? Can having multiple sites cause any problems?
Slogans are not copyrighted, they are trademarked (just like logos). If you want the additional protection, you will need to register the trademarks for each. If you are not concerned about the extra protection the you do not need to register them. Trademarks (in most countries) can be protected without registration (assuming of course somebody else hasn't already used/registered the mark for similar reasons.
what about the llc protection, if you have teh llc for teh main comapny, will the domains and websites under it hold that llc protection too? Like say you mention that abc media llc is the owner of this site example.com?