Dunno what platform you are on, going to assume PC:
1) Week 1 (this is day 1-7)
2) Day 8-14
3) Day 15-21
(Game locates your save files automatically from one package to another, no need to do anything.)
You can play the standalone specials as you see fit.
Also you don't need to pay per file, just pay once like say for example $12, and you get access to everything 12 and under (in this case, everything)