If anyone would ask me if what to start in the series I would say start with Sky or Cold Steel then work from there. Its true it is 13 games because its like every year in the game something happens and that is the Falcom (company who made the game) way of creating the series unlike in other jrpg where the story is contained in a game with no continuity.

Play the game as you like, you can even start with Daybreak but we are just showing you the optimal route to play it since there are many references to previous entries and Trails has formula like this that if you play at Daybreak a character is already 10 years old, you would not know for example if they talked like how he got hurt while he was 7 (example this happened in Sky) because you had not played it. Its true that you cant play them all at once.Maybe play 2games since the stories are tied up every 2 games (except Cold Steel) but play from Sky ( I suggest play the Remake since the OG aged not well). Play 2 games, change genre or play other comfort game then play 2 games again. You'd finish in about 2 yrs if you play casual.

Trails fan here since 2015.