Ghost themes don’t have custom fields for posts. (There are a small number of sitewide custom fields, but they don’t solve this problem.)
If I had to build a jobs board on Ghost (which is probably the wrong tool for the job), I’d think about each job post being a Ghost post. I’d use tags for location (for broad areas, not specific zip codes), job type, and salary range, which would make it somewhat possible to filter and sort job posts. And of course, if you were running a job board, you’d want a way for users to submit jobs, right? You could build that with a form on the site that triggered a cloud function that created a draft post.
But really, this is trying to fit a square peg into a round hole. Ghost is a blogging platform, and if you’re talking about content that looks really different from blog posts, you may be better served by a different platform.