Login should work again. Problem was in non-setting sessions. This was resolved by adding middleware "web" to admin group. Thanks to great documentation for NOT MENTIONING this pitfall!
Initilized package for creating modules. This still needs more testing to see if this is the real and best solution. However, I was able to generate module, so it seems promissing.
Add phpmailer and model generator into composer.json file. On server side, packages will be installed using composer, so that's the reason, why they are not in tree.
Michal Kváček