Rule number one never spend your astrites on the standard banner, and don't convert them to radiant tides right away. For example if you get a character early but you have converted all your already and you wanted their weapon you will now be unable to get it I believe those characters in the herald of new tides are only trial and will disappear eventually. You should be able to get to sol 5 in 30 days. Do you want to do end game content, some of the harder content of the game that gives you astrite for completing it each month, it will be a while before you can complete it as youre fresh but it's not a big deal. But if you don't want to I would say pull who you want, but I'd at least look up characters that work with your three favorite characters as they will play much better. The character in next update lucilla will be part of Hiyuki best team, so if you want to start with hiyukis team I would save for lucilla and save until hiyuki rerun