I’ve searched the archives, as well as a general internet search, but the terms are difficult to evaluate, especially at this late hour!
I’m curious to know three things:

Why do the numbers eleven and twelve have those particular names while every other number in that range (1319) simply has a teen suffix? Why the special designation in a base10 number system? Incidentally, in the Chinese base10 system, eleven is “ten one”, twelve is “ten two”.

Why are the numbers 13 through 19 pronouced digit first, tens second? (fourteen, nineteen) While every other tens grouping uses tens first (twentyone, ninetysix).

Do the names of the digits have any particular significance beyond their designation as a point on a number line? (When you trace them to their root name, i.e. seven to sept, and so on)