Many event eidolons quickly become or are obsolete, Kyuki is a prime example of one, having both a weak passive and bad summon skill. Eidolon passives only effect your kamihimes and only if they're on the main slot.
The bow isn't intended for you to be using on your water team, although you can if you don't have anything stronger. It's better in the long run over the eidolon because one cannot control what they get from gacha, aside from miracle tickets, so you might end up getting several good wind himes in the future, enough to make a strong team with, so it's not a bad idea to try to event SSR weapons as you'll likely draw a variety of different himes playing the game. Also, using anything aside from a dark or light team, it's reccomended to make a secondary team, to deal with elemental weakness, unless you plan to use your water team on thunder events.
The hime guaranteed ticket is pretty high priority but the regular tickets are on you. Soul P is only worth getting if you have everything else you want from the event. If you're really in a hurry to unlock Mordred, D'art or related required souls and maybe Joan, then feel free too, but anyone else will be a waste unless you have excess mats to use. Soul P becomes completely useless after you get all the souls you can unlock with it, even more useless than a never used event eidolon, at least she gave me some jewels. I'm sitting at 2.5k Soul P with nothing to use it on and there is nothing in the future to use it on from what I know.