Links to offical Sony Pages
Take a look at the LineageOS Wiki for some great developer-focused articles.
Visit the AlaskaLinuxUser on YouTube - there are video guides to building for your device, learning about compiling, and lots of other helpful tutorials.
Tools that will help your development progress.
Common tools and zips that are needed for the SODP ecosystem
Flashing latest stock firmware
The Open Devices Corner is a community documentation page about Sony devices and Android building and internals, maintained by a volunteer team.
It contains a whole lot of nice Guides with more in-depth articles but also some references like a technical overview of all supported devices, and a Developer Diary section where smaller and day-to-day findings are noted down.Sample selection
On Xperia 10 (ganges platform) and Xperia XA2, XA Plus, XA2 Ultra (nile platform) devices, you can run a functioning Mainline Kernel with the postmarketOS Linux Operating system. There was even a nice Phoronix article about the success of the effort.Mainlining resources
In case you are interested in SailfishOS, take a look at the project documentation of Sailfish OS port to Sony Xperia Tama devices.Official Jolla guides
Ubuntu Touch guides
Official documentation available at docs.ubports.com.
Official documentation available at docs.halium.org.