How to customise delivery options and the checkout page

Hi,

I’m not finding it easy to edit the checkout page. I want to change the layout and add in a few extra bits. I would like 2 options, Free pickup and Local delivery. I would like it when, you select local delivery, either a message underneath appears or a popup appears and asks for the post code, and if the post code isn’t on the list, a message advises them that they can’t have local delivery ( and it has to be a minimum of ￡5 spend).

I currently have it set up so Free pickup appears but you have to type your post code in the form below and the option only appears for delivery if the post code is eligible, this is very messy and not clear to the customers.

Please can someone help.