In terms of the summoner spells, flash + ignite is usually the way to go, however exhaust can be used against champions like zed, and yasuo and be fairly useful against them. Barrier is also good to take against champions like veigar, Sandra, etc, to avoid dying from their high burst damage.

Yasuo is generally a harder matchup for Ahri, his windfall will often stop you as counters basically every ability you do, and he can tell fairly easily if he needs to windfall by Ahri S spell animations. Playing against him is usually best to rush Seekers armguard and upgrade to zhonyas when needed, (same with zed).

I'd probably have some armour in the runes, or at least one for against ad and one for against ap.

Ahri charm was nerfed quite a while back, lowering its damage, making w generally the better option for maxing second over e.