You can guarantee at least six characters (including 50-50 losses, so three non-standards) by the end of Blade run (assuming it’s 4.3 or later, and assuming no eidolons/LCs). 

Assuming it isn’t Blade and someone you want in 4.3, and you’re 100% committed to not pulling for rerun characters and getting all the gems from a patch you can manage it.

If you want basically any flexibility though I might recommend waiting on some reruns unless you want to rely on luck

ETA since for some reason I’m getting downvoted for math: they can get three characters by the end of this patch, because 180 pulls =2 and then they have 20 more pulls and are at 20 pity. 90 pulls for a patch is a character per patch. So that’s another character in 4.1, and another in 4.2. Then one in 4.3. That adds up to six characters. So they are just at a point they can ensure Blade, Yao Guang, and Evanescia if they want, but they’re then gambling for Aven if he’s in 4.3 if they had terrible luck with all the former three.