Some interesting new info here;
https://www.starwarsnewsnet.com/2018/04/interesting-new-bios-about-the-main-characters-from-solo-a-star-wars-story.html

L3-37:

A “self-made droid”, L3-37 has cobbled herself together using an assortment of components from astromechs, protocol droids and countless other robotic sources, devising her own form and function to become something quite unique – with an impressive AI to match. L3-37 is Lando Calrissian’s enlightened navigator and co-pilot. Her programming makes for an indignant, spirited and somewhat eccentric companion, who cares deeply about droid rights. With a mind of her own (after all, she built it) L3-37 is subservient to no one.

Plus, a fair bit of info about Han’s youth and Corellia in the new EU:

Times are tough under Imperial rule, with planets across the galaxy feeling the pressure of the Emperor’s iron grip. One such world that has seen better days is Corellia, transformed by the Galactic Empire into one of its principle starship production facilities, it’s famous shipyards now churning out TIE fighters, Star Destroyers and many other weapons of Imperial domination. To survive the harsh reality that has befallen his homeworld, a young street thief named Han spends his days running scams while working for a notorious Corellian gang, stealing what he can and cutting deals on behalf of his ill-tempered crime boss. Han is unrefined, reckless, and continuously getting himself into scrapes – then improvising his way out of them. Never one to plan too far ahead, Han goes where opportunity calls. Determined to become “the best pilot in the galaxy”, he enlists in the Imperial navy only to find himself kicked out of the flight academy for “having a mind of his own”.