Do I have to choose a lineage or is it optional
Completely optional. You can be a bog standard Human is you wish.
Thanks for the information
I would reccomend starting with big standard human (easier to phys-rep).
There are methods for changing in play, some temporary, some not.
That also opens the option that if you play a second character, then a different lineage will certainly distance your second character from your first one, visually as well as thematically.