Doubt they'll do a graphic adaptation of Ahsoka, or at least not for several years -- they already have many stories they're trying to get out the door. About the only adaptations I expect any time soon are of the movies.
That said... The standalone miniseries collections would be good -- Darth Maul: Son of Dathomir, Kanan, Obi-Wan & Anakin, Han Solo, Princess Leia, Lando, Shattered Empire... And if you don't mind installments in a story that hasn't ended yet, the ongoing-series collections are quite good -- Star Wars and Darth Vader ran concurrently, so I'd recommend reading them together. The Vader series ended at 25 and the Doctor Aphra series picked up from there, so I'd still alternate. There's also the Poe Dameron series, but since people are so polarized on the new films, I'll only recommend that one if you like them. *heh*
As for the stuff that is in the Legends category, anything from the thousands-of-years-ago timeframe. Golden Age of the Sith, Tales of the Jedi, The Sith War, Knights of the Old Republic, Fall of the Sith Empire, Knight Errant... The period is unlikely to be visited in the new canon anytime soon, and the Story Group are fans of those works. References have already shown up in the new canon, so I feel it's safe.
--Jonah