i've been wondering this as well and i think they will come in a future update i don't know for sure though
Complete weekend 1 after that you can play as pico.
They changed it to where you don't have to beat Weekend 1 I think. At least I didn't have to do it on mobile
Its still the same in pc.
Press tab in freeplay to open the character select menu (after completing weekend 1)
yes but that is only 2 out of 9 characters
More of them will come in the future updates with week 8 (week 8 not weekend 1)