hi, 
1. Those .m2ts files may be created without any compression of video and audio?
yes.
2. Is there any possibility to choose default audio and subtitle track, which will be automatically choosen during playback, without need of choosing via remote?
for the m2ts, maybe cannot specify the default audio, subtitle, maybe set the first pid for this stream can make this as default by some player. and you can try it
3. May I choose more then 1 audio and subtitle track in such process of creating .m2ts files?
there are some little work to do for this, in the engine, this is not any problem.
I have tried Blu-Ray Ripper to .m2ts, I have checked subtitle Polish and audio English on my AVATAR copy. Everything goes OK, but when I play the .m2ts file there are no subtitles shown, why? What I am doing wrong?
what player is your using, current if you select subpicture, which has been convert to idx/sub, not provide remux mode now.
thanks.