Ho to customize the Thank You page?

Am I only allowed to have one thank you form for all my forms? I'd like to customize each thank you form. It seems the same pop up TY is being applied to each form.

Also I can't change the text size and font - any suggestions?

No, each form has its own thank you page, you are able to edit each thank you page as it is one different for each form, you only need to click on the thank you icon, you will find it on the top toolbar in the Form Builder:

As soon as you click on the icon the thank you wizard will be displayed, there you only need to click on edit text:

Then you will be able to change everything in the thank you page, the text, add tables, images, add your custom text as well as format it as you want. 

I think with change the font and the size you are referring to the text in the thank you page o you should be able to do it on the wizard, here is a guide that will help you with that as well: http://www.jotform.com/help/211-Setting-Up-the-Thank-You-Page. 

If you are referring to the font and size of your entire form, then these guides will help you: 

http://www.jotform.com/help/185-How-to-Change-Form-Fonts

http://www.jotform.com/help/186-How-to-Change-Font-Size-on-Forms

You may also do this using CSS code, this is an example of the CSS that you should use: 

.form-all{

 font-size: 20px;

font-family: Arial;

}

This guide will help you to inject the CSS code: http://www.jotform.com/help/117-How-to-Inject-Custom-CSS-Codes. 

Here is a link with more information about fonts with CSS: http://www.w3schools.com/css/css_font.asp. 

Hope this helps.