Well first of all if you are going to be using manual shooting, I'd suggest you to use 0 pass assistance as well. Reason being you will get use to the logic of aiming manually better, since your passing and shooting will both give you similar muscle memory, you just know how to aim intuitively when in front of the goal.
If you use something like 2 bars assistance but use manual shooting, you'll have to switch gears all the time, since the logic in aiming behaves in different ways.
The only problem I have with manual shooting is it's difficult to score open nets from tight angles. Quite often you'll just be watching your shot go straight for the corner flag or even worse. You essentially have to measure your shot and aim right between the posts.
Start with using the aiming guidance (arrows). Once you get used to it, you can try turning it off. I find the arrow guide to be distracting and actually limits my play, with me being obsessed with getting the arrow to aim exactly where I want it to. When in fact, there a lots of passes you do not need the kind of pin point accuracy. Turning those arrows off helps you play in a more relaxed way when using full manual.