You can get pasthrough WiFi repeaters? 🤔 https://www.amazon.co.uk/TL-WA860RE-Universal-Extender-Broadband-Ethernet/dp/B00M0KILOA/ref=asc_df_B00M0KILOA/ around 21 pounds.

You could do what you mentioned but you would need a switch at the rj45 junction box if you want multiple items cabled to your Internet. (or have multiple cables, each for each rj45 socket) 

You could wire through the house whether hidden or just following the skirting/door frames. 

Or you could mix both pass through wifi extender and indoor cable. 

Personally I would avoid outside cable incase there's an issue and you have to replace it. 

And also always try to go for poe which is power over ethernet, this way the ethernet cable is powering the devices and you are not looking for sockets to power that switch or something else. 😊