Are there some recommended TV models for installing and running self-made apks (or other extensions)?
If you want to upload and run your own app, Sony TVs and Philips TVs seem to currently be the best options, as they support sideloading applications. Samsung (Frame TV) allows for sideloading, but comes with limitations due to its Tizen OS (Smart Hub).
LG TVs do not support sideloading apps, users can only install apps from the LG Content Store (webOS). But there’s a hidden service (code 0413) with a menu that provides various settings and options, which are not available in the standard user interface. Or try out the Developer Mode app (not tested yet).