Go buy a Blade Nano Qx before you start on something with power like your 450. Put it in manual mode and practice. If you can fly the nano in manual mode with no problems then make sure you can fly your 450 in manual too even before you start trying to do flips.
In the beginning I set a throttle curve so that max was about 88% and my min was about 15~20% thrust (have this bound to a switch so you can change back and forth or even to what mode you are flying in). This way when I did a flip and reduced my thrust it would not die on me and punching it to full would not have one motor over power others. This allows for very smooth acrobatics imo. Also go corner to corner to start as it tends to be a quicker maneuver. Then later on, when you figure stuff out, you will be able to do a regular flip forward or backwards. Rolling depends on what you are flying. On my 350qx I didn't have to reduce thrust much if any to get a good quick roll, just push the stick all the way over until I am back where I want to be.
Start practicing at a high altitude this will give you time to recover or enough time to switch modes quick enough that the auto level would do the work for you. Another great reason to start with a Nano or even a 180qx is that they are durable and parts are cheap. I still fly mine in front of my house before and after work just to practice. What you learn there translates to the larger multirotors. So much so that it makes flying the larger ones boring and stale if you are not pushing the limits of them.