There are a lot of things to think about when it comes to time travel. 1st: don't worry too hard about messing with the time line. to quote The Doctor; "Time is a ball of wibbly wobbly... timey wimey.... stuff." which may sound like non-sense, but isn't. you see if time is one hard line then that means that what has happened and what will happen is set in stone... sort of. This includes you time traveling. so if you went back in time and killed a butterfly, don't worry. you always went back and time and kill the butterfly. the butterfly was destined to die by your hands. HOWEVER! this does not mean you are safe to do what ever you want. If you try to do something that you already have knowledge that it did not happen (e.g. go back and kill Hitler), because of that fact that you know this does not happen, it will result in one of two outcome. 1: It simply will not happen. you will fail. or 2 and this one is more severe: you will create an unstable paradox (will come back to what that is in a momment) and essentially back the universe. The 2nd thing you need to know is what paradoxes are allowed and what aren't. the bootstrap paradox is allowed. this is one where information (such as the book that told you that you are in a liner time line) has no origin. you know that the time is 1 line cause future you told you, and he know because of future him told him etc. next, the Temporal paradox is NOT. this one is a broad term meaning you can not go back in time to cause you to not to be able to do soothing that you know you did. this includes (but is not limited to) killing your own grandfather, destroying the time machine before you ever found it, crossing your own time-line in anyway that you do not remember happening, and of coarse.... killing Hitler What are the consequences to braking Temporal paradoxes? well imagine you have a single strand of uncooked spaghetti. now imagine you try to make 2 strand of spaghetti of the same length by splitting it down the middle (aka try to make 2 timeline out of one solid line). What will happen is the strand is going to snap. what does that mean for the universe... I have no idea. I would recommend that you don't try and find out.
I'm sorry, but i had to reformat that. It was actually hurting my eyes to read.