Valentines Gacha

Jack or Jeanne are both great options for you. (Jeanne might be better since you have Bride and Tamamo, but King Hassan removed most of the Jacks from my support list.) If you don't get either, you can try again during the class-based summoning campaigns come March and August; Jack and Jeanne share rate up, so you'll be pretty sure to get one of them.

Definitely consider Waver. :)

Among the gentlemen, Karna, Enkidu, and Cú Alter are the standouts---Cú especially, since he's story-locked and you'll never get a spook. But the guys are all on shared rate-up so I don't recommend rolling for any of this until Chaldea Boys in March because the odds you'll get a unit you don't want a pretty high.

Since you are going into it with limited rescources as you said, only 60 SQ and 20 tickets, you’ll probably only want to focus on one and I would go for Jack. She is still arguably the best assassin in the game. Best star gen of any servant and the female niche on her NP which covers a lot of the dangerous riders.

Jeanne is helpful in arts teams by giving you the added arts cards to work with, so you’ll get to fire off some more NPs, but her kit is still just average. And you already have the right pieces for great arts teams without her. Her NPs team invincibility is definitely a nice effect, but I don’t think you need her. Assassin looks like where you’re lacking the most and taking the chance at getting the best in class over just another arts servants to add to a team full of good ones makes focusing on Jack the choice I would go for.

Jack looks like a great choice, your other classes are well represented and jack is an amazing servant.

Jeanne is less useful unless you like zombie teams or are tackling a challenge quest and need serious stamina.

I can't tell if you already know this, but saying a "secondary goal" implies that if you don't get MHXA, then if you get the other that's OK. But the way it works is that by rolling on a double banner, you reduce your chance at MHXA such that either her or the other servant will have equal odds. You're not overall increasing your chance to get any 5*.

I think the last time I looked at a double banner, the probability of each 5* was something like 0.45% instead of 0.7% for a single rate-up. At least that means you'd be less likely to get spooked, but it still means that if you would much rather have MHXA over the other servant, you might just as well roll on her single banner.