First, I would like to say what a wonderful mother you are! You already have what it takes to be a wonderful mother! I am a mother of 4; all of my children are adults now. I remember worrying about how much is too much of this or that, lol. I miss it. Bless your heart.
In my opinion, it is never, ever to late to start reading! It is always better late then never. Developmentally, according to studies and science, 5 yrs old is when the internal "processors" change and are not as fast as the 1st 4 years. Things sort of "switch gears".
So, there you have the opinion of an experienced mom. You have some facts you can check up on scientifically speaking. But, we did not give the best source of information a voice or a chance at all. Who or what is this source you may ask? She is an expert. Want to see her? She is in your mirrors.
This is a very special time, I hope you cherish it. It goes so very fast. In this time, you are not only the teacher; you are also the student. Life has this awesome synergy, a way of showing you something. You have an incredible gift, it is called "Mothers Intuition"; each mom has it. Some just don't know or understand how or if they should listen to it. Only life and time can show it to you. You do have it though! Trust your gut.
It is okay to make mistakes. It is how we all learn as you will see in your baby. You are already off to an incredible start though! I know because you care enough to ask. If you try something, and it feels wrong, modify it. If you like the way something is done, and you get 150 different people saying "no do it this way, or that way" research it. If you find no harm and you like the way you do it.. stand your ground!
No one knows what is best for your baby better than you. Opinions come a dime a dozen. Yours ultimately is the best for your baby, and for you!
I'm here for encouragement if you need more.. You got this!