You can visit LineageOS website. They support wide range of devices and then you can buy one .
Flashing google apps is optional and you can flash Lineage OS on supported device in a simple way
Unlock the bootloader (if you are planning on buying a phone, make sure OEM support bootloader...
Home directory is not private.
Ubuntu 21.04 made home directory private by default on new installation.
Try Ubuntu 21.04 and dont connect your WiFi network or LAN network and check if you still get tmp files
It will happen, if you have connected to VPN and network and your PC turn off due to power failure..
Issue is related to DNS server so internet will stop working untill you connect to VPN network again (this may overwrite the DNS server)
I also faced internet problem when my PC turn off due...
Can you try USB tethering and verify whether internet works or not ??
I had faced such problem before and there is no solutions to that except reinstalling the OS (At least in my case i was running Ubuntu 20.04, 21.04 & 21.10 and couldn't able to find proper solution to No Internet issue)