How to gain proficiency in all skills at level 4:

It's very simple. Be a noble or some other background that gives skilled for 5. Then, be a human and take skilled as the feat for your resourceful trait. That gives 4 more for a total of 9. Then, be a Bard. 3 more at level 1 for a total of 12, and at level 3 become college of lore for 3 more, bringing us to 15. And at level 4 take skilled again. That brings us to a total of 18 and expertise in 2.