@Effinrayjay 

Your existing Powerline adapters will work with the AX1800.  They aren't wireless adapters so there is no signal that can be interfered with or that you would need to clone.  Its essentially just an extended ethernet port.  Sure the PA4010 is Fast Ethernet only so the max possible speed would be 100 Mbps.  If you are looking for a better Powerline then I would recommend the TL-PA7017P Kit This Kit uses a more recent protocol for powerline.  Has a better maximum transmission rate between the nodes and offers Gigabit Ethernet ports.  Plus it offers power passthrough so you can still use the electical outlet the unit is plugged into. 

  @Effinrayjay 

That is more difficult to answer.  That is because it is a multi-factoral concern.  Just like Wireless, powerline has its own set of barriers.  These include distance, number of jumps through the panel, noise on the powerlines, the number of applianced on the same circuit not connected to surge protectors. These all wil reduce not only the throughput between the two units but the speed  powerline adapters get over the internet.  Take a look at this post i made from a few years ago that explains it in greater detail and if you have any other questions let me and the community know.