There are many variables that come into play when establishing rewards and pricing. The more options you add the more complicated it becomes. I would suggest a "less is more" approach to start as it will be easier and safer to set up and better for backers to make decisions. There's a lot to be said for limiting options. Remember that you can always add reward tiers later.
This really aptly sums up creating rewards and pricing! It's always a confusing part of the campaign and includes both an art and a science especially since you as the creator also has to take into account things like shipping costs, logistics charges, production and manufacturing at different quantities, etc.
In short, there are really no "right" answer as it really depends on the campaign and what type of "thing" you're launching.
Here are the different concepts I love going through with creators planning out their rewards:
1. Price anchoring - create a high anchor price so everything else looks reasonable
This usually is in the form of a "Kickstarter Special" that is at the highest possible discount available.
2. Scarcity - create a limit to supply so people experience FOMO i.e. only 150 available at this price tier
Even though you have more rewards leftover, you want to always create a limit to supply. If you have 50 total rewards (like OP has), you can release 10 at a time so when people come to your page and see only 2 left to claim, they want to jump at it. Once you get to 1 left, add another 10. Keep doing that until you get to all 50 total rewards. You can even use tools like StockLimits.com to automatically do this throughout your campaign rather than checking back to keep increasing the quantity as they get to the end.
3. Urgency - create a limit to time so people experience FOMO i.e. “get it now or else prices go up!”
This gets people going big time. That's why sales have a start and end date. There are those people who plan for it (early Black Friday shoppers for example) and others who roll in right before the clock hits midnight and the sales disappear. Give them reason to set their clocks and get ready for your rewards!
4. Paradox of choice - the less options we have, the better ([Choice] produces paralysis rather than liberation. With so many options to choose from, people find it very difficult to choose at all. - Barry Schwartz)
Keep it super simple. If you want to release a book, like OP, distill it down to ONE main reward, and tier it into different reward levels. Anything else beyond the "core" product (aka the book in this case) is an add-on or a stretch goal that you can add later on in the campaign. If it's two different version of a product, create a version A and a version B reward and tier up pricing from there. Include an option to get both! But in the end, make everything as simple as possible for your launch!