Well, personally in terms of treasures to focus on. The ideal goal after getting Roshi would be to pick up Edo Hashirama from the Great Ninja War treasure which is probably around 2.5k pulls or so. Not entirely certain on the exact numbers. Edo Hashirama and Kurama Naruto are two of the most used characters still in China IIRC as far as treasure characters go.

In terms of event only characters. Try to pick up Edo Hiruzen, in fact I strongly recommend it. Of course the choice is up to you either way.

As for the Five Kage treasure, you could probably put some focus here I suppose if you really wanted to, but Ay 4th Raikage, and Susano'o Sasuke won't shine as well as they used to until Skill Experiment. Not suggesting at all that they are bad, it's just they are being out performed mostly by Kurama Naruto currently.

Anyways, I hope this helps.

P.S. Try to save up 300 Seal Scrolls always before using them and make sure to utilize the Ninja Recruitment events. Good way to gain some ground with a good chunk of additional pulls.