You can put in the form itself and use script in clientLibrary.

Need to check the form for any reference to javascript(vkatoch07@gmail.com). For debugger, you can disable it in Acrobat choosing from Edit> preferences>Javascript

Put various app.alert("test1"); inside your script to check at which line script is breaking. There might be an issue with som expressions in the script.If you cant find it then share your form with me(vkatoch07@gmail.com).

Return the result as true (or any flag as per you) if the request is executed successfully in AEM workbench and then based on that value hide your field in the form.

Your developer might have set the minCount to 1 for the table, if they set it to 0, they will be able to delete it.

You need to extend the pdf with a reader extension service or use Acrobat to save data entered in the pdf. 

Need to check the form, see if you can convert some tables to subforms with fields like table structure, if that reduce size.

10 mb is huge size for xdp, even over 10mb LCA file create issue while deployment.Is it only the number of tables contributing to size or you are also using images in xdp. 

I think there is no such property, to achieve this you need to write the script in the click event of the link/button.

Make sure you have made a flowable layout for the form and wrapped the fields inside the subform with a flowable layout. Some best practices for html5 forms:https://experienceleague.adobe.com/docs/experience-manager-65/forms/html5-forms/best-practices-for-html5-forms.html?lang=en