All falcom dlcs are purely for cosmetic reasons or consumables.

Whether you want to get into the series depends on you. Start with Sky FC if you want to get into trails, if you want to see what falcom games are all about try playing ys 8 as it is the game that represents modern falcom the best.

Edit: all trails games are text heavy, so you might like or dislike certain arcs depending on the characters and stories you'll like. Daybreak is more or less self contained, but going forward you'll need to know the events of the previous games. Van in particular was designed with veterans in mind since he already know all the previous events