Stay calm and we can help. First did you do a factory reset before updating or have you done one since updating? If not I would recommend that as a baseline course of action to clean things up. Next you can go about doing your Google stuff and then just do the Google updates first, then add your non-google apps to make sure they work properly, try one at a time. Its time consuming but so is dealing with something that is erratic.
The biggest issue is Google hands off Android (Lollipop) to the OEM's who then add their layer of cruft, make changes, and then the carriers (US) come along and want things disabled, removed, added, tweaked and then they have to test it for months and make more tweaks. So its not Google's fault, its not entirely Samsung's fault, but the Carriers have to meddle with something they should not in the first place.