The range depends on the existing listings (to avoid empty search results), for example if there are listings with $1 and $1000 price then the range will be set to 1-1000, since searching for 1000+ would return no listings.
If you mean header image then by default properties/listings pages do not have it. If you mean a single post page then you can remove the featured image for a post to remove the header image or you can use this CSS snippet too
.single-post .header-hero{
display: none;
}
You could try to use the bbPress plugin. I also recommend creating a forum on a subdomain because keeping it within the same site (if you have many listings) may slow it down (since WordPress stores everything within the same database tables).
Or you can try another forum solution like Discourse which has more features like voting, marking topics as solved, assigning staff to topics, etc.