How do I deal with Buddhist teaching's complexity?
"Im feeling very overwhelmed by the sheer amount of different things to remember and practice"
"*****"

No need to, that is why it is called gradual training. You take only one step at a time. In regard to four foundations of mindfulness you just practice the in and out breath until you master it.Then make an attempt to observe the five precepts. Then everything else will put in to place automatically.