I'm a new DM and I'm running a group of new players. We're a pretty casual group and they haven't bought books or dice, and aren't very invested in the game. Is that normal? How much should I ask of my players?
This is normal, but also a warning sign.
You have not mentioned the gaming system that you are using, but typically tabletop role playing requires a greater level of engagement than a board game club. At a minimum, your players will need to be able to:
Meet on a regular basis. If you meet too infrequently, your players may be unable to follow the story and will have trouble retaining game rules and character role play notes. From my own experience, meeting once a month is pushing it - once every week or every other week is ideal.
Understand the rules. You can get pretty far by explaining the game as your players play it, and this can be a good primer for your players to get a big picture before they trudge through the rule books. At some point, however, they will need to actually read the game manual.
Create characters, and understand their character abilities. New players often underestimate how much time this takes. As a new GM, you will likely be too busy managing NPCs, keeping your game world straight, and applying a vast array of rules to constantly chaperone your players. If your players do not invest time into understanding their character's abilities, you will inevitably be stuck having to remind your 1st level druid that they can't wildshape into flying creatures, making sure your spellcasters have sufficient spell slots, and keeping your martial classes from adding modifiers to everything. You might be able to mitigate some of this with pre-generated character sheets, but your players may balk at this suggestion: ironically, low effort players are no less likely to want a custom made character.
You need to figure out if your players are willing to do these things. Schedule a session zero and tell your players what their responsibilities will be, what will be expected of them. Do not try to soft sell these expectations out of fear that you might scare them away: if this is too much for them, it is for the best that you let them go (both for the game, and for your friendship!)
The above all relates to time investment. The question of whether your players need to invest cash money into the game is logistical. Plenty of groups get along fine just sharing books and dice, or using digital material. I would need to know the gaming system you are using to offer more advice on this.
Books are expensive enough that, if people are new to the hobby and just trying it out to see if they like it, I don't really expect them to rush out and buy the books right away. Often, in my experience, what happens is one person will be enough into things to buy whatever is necessary and share with the group.
If the players are more experienced and are at the point in their life (i.e., not high school or college students) that they have a little discretionary cash, I might look askance at this, but honestly not much.
Dice are actually the opposite-- they're so inexpensive that I always have enough to go around, so it's not an issue. I have my good dice and when needed I have my pile of junk dice.
As to "not invested" that really depends on what you mean. But the answer is likely to be, "Yes, if not normal, than within the bounds of what many people have seen." There will always be some of us who are very into the game, gaming, and the hobby as a whole; but there will always be those who are casual about it, too. If they're not invested monetarily, but are active and creative participants, that's a cross I personally could bear. If they're not invested in the story we're playing through, that becomes an issue for me. What does need to happen though (and it will, one way or another) is to decide or figure out what level of investment from your players you need in order to charge your creative batteries.
It is only when they're not providing you enough, that you have a problem. (And likely, a different question.)
It depends on you, most of all.
I interpret your question in the way that your players might be joking during and about the game, fooling around with NPCs and such.
From my experience, the GM has great influence on setting the tone here. I'm in a Pathfinder group for over a year now and never bothered with buying the books. I'm reading the information I need in the online version and ask my GM about specific details and how he personally wants to handle certain rules. We usually start a round by telling personal things and than slowly drift into the game. Sometimes, we even continue joking dureing the game, but usually try to play it like the characters are mocking each other about their previous failures etc.
But, there is usually a point where decisions have to be made, a tense scene requires attention or a fight starts to get interesting and the out-of-gamechatter usually fades out. How much it does depends on how you want to handle it. If you let your players have fun and let their characters get away with murder, the will usually play more casually. If you start making decisions more impactful and the game more challenging, you usually force them to pay more attention.
At least, that's my experience. The specific handling heavily depends on your group.