Crystallized Lores and where to find them

There is one every week or month in the rare prism shop
Also quite a few events have them as rewards one way or another

level up to 10 the skill of 1 or 2 servant you really like,, those servant you like to play (like my cleo or cu alter), and the other for game play.
then other servant bring them to 6, or 9 if the skill scale really well..
Thets the my golden rule.
Also, alweys level up to max your first SSR. he deserve it.

Just lv10 Elizabeth Brave 3rd skill, that's the only viable course of action.

I checked out your Servants page. You should definitely max out all of your Waver's skills. Lancelot Saber too, if you find yourself using him a lot, he's just such a beast. Honestly, though, all the currently available EN Servants' pages have commentary about their skills and how useful they are. You can just use them as a guide for what skills you should be prioritizing, comparing it with your own experience of which Servants you find yourself using the most and consider to be the most generally useful with the typical strategies you employ.

QP limitations will probably prevent you from getting every one of your servants to 10/10/10 anyway. It's a horribly expensive endeavor. By the time you actually accumulate the necessary QP and materials to 10/10/10 one SSR servant, you'll probably have another 3 crystal lores.

Most events have them as rewards or store. Just be sure to get them all.

They aren't quite as rare as Grails. Practically every event has at least one lore, and sometimes as much as 3. If you can actually run out of lores before you can run out of QP, then I'm pretty jealous (it takes like 170,000,000 QP to max 3 skills for a SSR servant).

As far as how you should use your lores goes, it's up to you, but I'd spend them in the way that makes the most sense. You'd probably want to prioritize servants that you use the most, and skills that benefit the most from a cooldown reduction.

Waver should be your top priority. Reducing the cooldown on his skills can greatly impact your gameplay. Maxing all 3 of his skills is highly recommended. Not only would it make your fights easier, but it would greatly increase the amount of friend points that you gain each day, because most people don't bother to borrow Wavers with unmaxed skills. It's just too easy to scroll a bit further down your friend list and find a maxed waver to use instead.

Other than that, it really just depends on which servants you use the most. But I personally wouldn't be fixated on maxing all 3 of a certain servant's skills, because a lot of servants tend to have a skill or two that don't really benefit as much from being maxed. If you really want to get the most out of your lores, then it might be best to pick and choose the skills that benefit the most for now.

For example, you mentioned that you want to skill up Jack. Her 1st and 3rd skill are great to max. Her 1st skill is a massive steroid that also increases her star generation and np generation, so it's obviously great to get the cooldown as low as possible, so you can use it more. And her 3rd skill becomes a 4 turn cooldown heal, which is super useful, so it's obviously worth a lore. But her 2nd skill, while being a great skill, doesn't really benefit from levels quite so much. It doesn't help you erase buffs any better by being high level, and I don't think that reducing the cooldown will really impact your gameplay very much, because it's just not that common of a scenario for you to need to spam that skill multiple times in a fight. So I'd personally only max her 1st and 3rd skill for now, and then use the other lore on someone else who can benefit from it more. You can always come back and max her 2nd skill later, when you're feeling less strapped for lores. But that's just my own personal opinion, of course. You should play however makes you the happiest.