(I'm a freelance illustrator, and this is a n email replying to my/a customer)

May ICan you please understandlet me know how many pages you'll need for your book?

And how old arelso it would be good to know the age of the tartget audience will be as well?.

I'll use a proper style according to differenn appropriate style catered to the target audiences.

I will provide theyou with a quote based on the volume of the illustrations and the delivery estimates for your reference as soon as I can understand some basic requirements tohat will help me get started with the project.

It works but it is a very long sentence!

Should you have any questions or concerns, please also feel free to let me know again/feel free to get in contact.

Thanks so much!

Many Thanks

And how old areis the tartget audience will be as well?¶

"Are" and "will be" are both the same verb, you only need one or the other.

I'll use a proper style according to differentdifferent style depending on the audiences.

What you wrote works and is understandable, but this is a little simpler.

I will provide the quote based on the volume of the illustrations and the delivery estimates for your reference as soon as I can understand some basic requirements to help get started with the project.of the project. The quote will be based on the volume of the illustrations and the delivery deadlines.

This is a longish sentence and is probably better broken into two, or at least separated a bit by commas.

Should you have any questions or concerns, please also feel free to let me know again.

"feel free to let me know" is a commonly used phrase in English. You don't need the "also" and "again".