I'd make kimarhi a thievin' high level white mage, if I were you It takes a while, but it's immensely fun useful, and you actually use kimarhi in battle because of it.
thats what i did in my recent play through. i had some reservations about it at first (i usually just send him through rikku's grid and quit using him once he's at the end of it). i did his whole grid, started in rikku's grid to learn steal and use, then used a lv.2 key near yuna's dispel and reflect section of grid. (i learned cura by the time i got to home). it does take a bit of time and levels to do, but his high magic attribute seems to make his blue magic stronger, (i didnt know his blue magic relied on the magic stat like white or black magic does) so his fight with (SPOILER)yenke and biran was alot easier than when he was just a thief, plus stealing as much lv.3 key spheres as i could. i still use him alot, so the thief/white mage combo is a good choice. i also had yuna learn steal and use, but kept her in her own grid. never have too many thieves

It`s a good idea to put yuna through aurons sphere grid after your aeos get break damage limit, that way her aeons will become stronger.
does it matter what stats she learns for her aeons to get stronger? i thought their stats increase somewhat randomly as yuna's stats increase. will the aeons become stronger physically if i put her through auron's grid or more evasive if she goes through lulu's grid, etc.? ive played this game so many times ive lost count, but its always good to learn somethin new lol.