Is a studio logo considered a pre made asset? Or is it okay to use?  Im just wondering.

a logo shouldn't be considered as that as long as it does not interfere with game play

I think anything to do with your splash screen, credits etc are fine. If it's not really a part of the game then that's fine. If it's just cheap advertising in your game, I'm sure that's ok too, but make sure you have copyright usage rights!!

You can use your own logos in the game

Can we use any of the unreal sample project stuff?