The only sentence that does not sound correct is "I think too much over it." With that, it is important to point out that (though minor) some sentences can have a different meaning. I overthink things too much. - The "too much" may be redundant if you mean "too much" in the sense of "I am thinking about these things too much," because the "over" in "overthink" already implies the "too much." It only works well if you mean "too much" in the sense of "too often"/"all the time." Either way, the listener would understand it as "I think too much/too hard about things." "I think too much about it." - I think about this a lot. This sounds more natural in a conversation as "I think about it too much." "I think too much into it." - I am thinking too deeply about the issue. I am looking/reading too much into it. (common expression meaning "to carefully analyze"). It could also work as "I think into it too much." I hope this helps. Tricky question.

你写的句子不是地道的。I would say: I think about things too much. I think about it too much. 也可以说： Think it over. OK, I'll think it over. Think about it. No, I think about it too much. Look into it. OK, I'll look into it.

Second and third sentences (I think too much over it. I think too much about it.) are correct. The other two are wrong, you can't say in such manner. You can also use the following form: I think over (or about) it too much.