Need help

This can easily done with rules.  I put together a quick demo using a drop down control and a three separate single line of text boxes. 

Here is the form:

The choice control just has three options "Show 1, Show 2, and Show 3".  The rule on each text box only shows when the choice control has the correct selection.

Hope this helps.

Can you please me arranging checkboxes vertically as well

Depending on the form type will determine how check boxes will line up.  I have Nintex for on premise Sharepoint 2016.  The classic form style essentially allows you to drag and drop the controls pretty much where ever you want on the form.  The responsive form template, is a little more restrictive when it comes to control placement.  You can stack items on top of each other.  You might have to fiddle with it to get the lineup exactly how you want it.  Does this answer your question?

Yes, use the Not and Contains rule.  

Here is an example of the rule I used

Choice is the name of my multi-select choice control. You'd need to place this rule on each check box and select "Hide" within the rule.

Here is the actual form.

Hope this helps