Problem with conditional button

Hello everyone! I need help solving a problem with conditional button. I have to verify that 3 input fields were filled with only 1 letter in each. And I will have a button to validate these 3 input fields. However, the button should only appear after filling in the 3 input fields. I tried using some triggers to show and hide a layer, and in that layer I put a trigger to change the button state to Normal if the input fields are different from blank. My idea is that the layer is constantly checking the 3 input fields. But it's not working. I also want to know how to restrict the number of letters in each field to just 1 letter. I'm submitting the file for evaluation. If you can solve this in a simpler way, let me know how.