Literature on cardistry is a bit tough to come by. Honestly, my biggest suggestion is to master some necessary one-handed flourishes in both hands in order to acquire the dexterity to move onto the two-handed stuff.
Fox13's suggestion to check out the 'Big List of Tutorials' is the best go-to I can think of if you're strapped for cash.
If you have some cash to sling, there's Andrei Jihk's 'Genesis'.
Magic books. Books. Books. Books.
Let's see. DavidL11229's suggestion to check out the David England free video of what books to select is a great resource.
Don't forget to check out your library as there may be books there. I mean, why spend money if you don't need to. However, I will say that if you find something like 'Royal Road to Card Magic', you will be spending MONTHS on it if you follow the book to a 'T' and go hard charger. The way 'Royal Road' is set up is that the book acts as a bit of a mentor. IT's a bit of a dry read, but it's worth the read.
ALSO. Get corporeal BOOKS. Can't stress that enough. Speaking from personal experience, please don't get PDFs if you can help it. Because BOOKS don't crash. Your computer crashes, so does your magic library. Books only crash in a fire. Plus, books don't require a battery, plugin, or updates. AND, the best magic lies in 2 sources:
1) books
2) asking the right questions (which happens to be for free. Can't go wrong there)
Bobo's Modern Coin magic is a great resource for coin magic, if you so happen to divert and want to expand your magic knowledge.
ALSO, since you're still in school. If you so wish to do so. I encourage you to take a drama or theatre/drama class. Or a theater group or club if you really want to improve your magic. This is to build up your confidence in performing and being able to construct a character.
In magic, we are all actors PLAYING THE PART of a magician. The backbone of what we do is magic, the CORE of what we do is acting and performing.
To this end, (and I think I'm going to get my teeth kicked in for this) I believe that it is more important to become proficient in the performance aspect of magic than it is the sleights.
Say you purchase 3 tricks from this site. For sake of example: Break, Invisible Card, and French Kiss.
You become a MASTER that those tricks and you can perform them frontwards and backwards. If your character and performance is dull and lacking, your audience won't care what you do; no expensive trick will save you. I believe it is paramount to work on your performance and a creative script for your routines. There's a lot to magic other than the sleights. A lot of it is the 'behind the scenes' work that the audience will only see the 'final product' of.
As far as time to practice? That's all up to you, brother. I know you're in school and, more than likely, have a lot on your plate--at least a bit more than I do
You must find a good balance between what is important in your life and your newfound 'hobby'. No one is pressuring or pushing you to accomplish certain goals within a certain time frame. It's all up to you.
Take your time, no rush.
But be careful of showing your magic in school if you purchase or become great at a sleight--especially high school, I've heard more nightmare stories than good ones.
I hope this helps in some capacity. Welcome to magic. Welcome to cardistry. Welcome to Theory11. Enjoy the ride.