Proficiencies are chosen at character generation. 4 feats are also something all classes get, not something you get from the Rogue class.choices of 4 skill proficiencies
choice of 4 skills to get expertise in
choice of subclass
choice of 4 feats or ASIs
That is 13 explicit choices you have made as a Rogue-Assasin between 1st and 12th level and that is before you consider the choices made with your false identities, which are really only limited by the available time and gold.
And, no you don't really get to choose 4 skills to get expertise in, you get to get expertise in 4 of the skills you already have proficiency in. Wow. Again, be still my beating heart.
Talk about grasping at straws here.