Before you jump in, the first thing to remember is that the October ’19 changes only impact you once you reach the end of your current license agreement term. If that’s in 12 or even 24 months, then don’t panic (yet), but if it is in the next month or two, you need to get to grips with the new licensing now.
To note – the summary below is not a full and inclusive list. If you’d like the lowdown on every change in detail here’s some light reading for you. First, there’s the 60-page Microsoft Dynamics 365 License Guide, and then there’s the also the 60-page Microsoft PowerApps License Guide. You need to read and understand both guides to be truly expert.