Hello,
I'm Serhii Kniaziuk (+02 EEST)
First of all, thanks for the detailed instruction and archive with html look.
Regarding the plugin. Generally task is fully clear for me. I can create the plugin, which will import all the json data from the mentioned API and place it on your wp-site. There are different ways how to store this data as advanced content type, even using free PODS plugin (good thing to manage custom post types with custom fields with separate sql table especially for jobs, instead of placing jobs in general wp_posts table, where everything is mixed).
Also I will use the proposed design to output jobs list and each jobs. Responsive css-fixes with media-queries for low/middle resolutions will be provided.
Regarding regularly updates, we could discuss it further. I would ask you to detail a few things and would propose you different ways (from wp-cron to cron job from cpanel). But anyway, I think the list must be stored on the db. Lower server load and no dependency on source (if it's down for a while)
All of this we could discuss further, if you accept my proposal. The whole work would take 5-7 days.
Now, shortly about me:
I'm 9+ years php/js/html/css programmer, including base design and "psd to html" work. Created more than 30 wp-plugins and customized hundreds.. I'm new at freelancer.com (about two months), but already did a few wp-plugins. You can check feedback in my profile reviews.
So, if you have questions, please be free to ask me.
Thanks