Seyllana
I'm fine with Kael knowing Seyllana, I'll let you decide if it's just her youthful beauty version or if he has come across her in her crone visage. I'm fine with what you suggested. Alternatively, he's definitely worked in the shadier side of things, so they could have easily met up during something nefarious (either as competitors for the same thing or working together or forced to work together due to circumstances). I'm not sure that a situation where she botched trying to kill him like her short story went would be the best of ideas, although I suppose if he stopped her but didn't attack her then they could have become acquaintances.
Genevieva
I'm fine with what you suggested. Alternatively, he could have been anti-slumming it above his pay grade with a score of cash and been one of her 'dates'.
Gara
Perhaps...someone picked a fight with you which turned in to a less-than-fair fight, and Kael evened the odds a bit (not helping much, just like smashing one of the three or four jumping you)? If you don't like it, no biggie.