It's very good that people are earning money
I'm interested,do you write these books yourself?Or you hire someone?And if you hire someone,how much do you pay them?
And OP said in the first post that it is possible to produce one book per day,well,that book would be somehwere between 20-40 pages maybe?(IDK I've never written a book)
Oh,and one more question,does it matter if the book is 40 pages or let's say 150 pages?Is there a big difference between their prices and do people buy that small books?
When you are new you should write your first book(s) by yourself to make your own experiences with the whole publishing process and also with fiction/non-fiction writing, niche/keyword research and so on. Buy a A-Z guide about Selfpublishing to get an overview about the whole process and read this thread completely.
If you have success with your first book(s) and if you know what's working the next step is to outsource the writing to scale up your output ratio/income. If you have enough ideas/niches try to outsource as much as you can. The only limit is your personal budget and your skills/time to handle/market so much books. My own experience: I'm in this game since May 2014 and also have quitted my job for Selfpublishing. So I am doing it full time but I couldn't market 1 book per day permanently. You have to analyse the market for niches, create the covers, find good keywords, write the product description, format the book files, maybe promote your books on external websites, manage your own blog + email list, manage your FB + Twitter accs, read more about Selfpublishing/success/personal development and the most important thing: Have fun and enjoy to make money!

The primary goal is not to reach 10k/month. The way is the goal and you live right now. So you have to enjoy it right now. So I prefer to pusblish 2 books per week constantly but market them excellent. But I have much respect if someone is able to publish 1 book per day.
To your page count/price question: It only depends on your niche(s). Look at the competitors books in your niche and look at their page counts, prices and rankings. Then you can say: If I would publish a comparable book (eg. with 60 pages, with a comparable quality) I can sell my book for this price (eg. $2,99). But you can also say: If I produce a better book than my competitors (eg. with 120 pages, a much higher quality and so on) I can sell it for eg. $4,99.
Try to imagine: In the car industry there are different product classes. There are less quality cars for a low price but there are also expensive cars with a high quality and maybe some bonuses. Both classes are working because there a people with less money who want cheap cars but there are also successful people who mant to buy a Mercedes with high quality. But you can not sell a low quality car for the same price like the Mercedes. No one will buy it. Now compare it with your business: Your market is your category/niche on the Amazon Kindle Store. And there are eg. Low quality books for $0,99 but also high quality books for $6,99. But it depends on the niche (and the competitors) to decide what's low and what's high quality. Eg. If you want to publish a book in the medical category maybe the lowest quality has 200 pages and price of $6,99 and a high quality book has 400 pages and a price of $14,99 (just an extreme example). Conclusion: It only depends on your category/niche. For my current niche a page count of 60 is enough to sell my books for $2,99 (but this answer won't help you because every niche is different).
So, try to answer: What is the right price for a car? Answer: There is no right or wrong price. It depends on the quality you want for your money (and the whole car market/competitors who define what's the price for low and high quality).
Hope you understand it. Please read the whole thread because such (basic)answers are already given here for many times. If you are not able to read you will fail. The quality-price-ratio question is general knowledge. If you had thought about yor question you had to give the answer by yourself. That shows me that you are not willing/able to think alone. But you have to think alone if you want to be successful because there is no step by step guide with a guarantee how to make money. And exactly this mind set differs a successful business man and a general worker. Try to think alone about such basic question.