I watched the Bleach anime up until the last episode that was released, and I want to start reading the manga now, but I don't want to read and repeat things that I've already watched in the anime. So where do I start reading in the manga so that I don't get lost and I also don't repeat things that I've already watched? Also, do they leave anything important out in the anime that was in the manga? Because I don't want to miss anything and I want to know everything.
On you first question about where to begin reading, the question referred to in some of the comments is similar.
As to your other question(s) the anime follows the manga very well for the the most part, except for inserting several anime-only filler episodes, including two rather long arcs and some shorter ones, as well as episodes based on omake. So you don't have to go back and read everything, you won't miss much.
The answer best showing where the anime and manga differ, while also answering where to start reading (manga chapter 480 BTW) is the answer by https://anime.stackexchange.com/users/24/logan-m to this question: Which episodes of Bleach are filler?