You can do all this from the "Top bar" section of your admin panel.
How to add more links to the top bar
To add customized links to your marketplace you only need to click on the "Add a new link to menu" option. Fill in the name of the link and add a URL to indicate where the link will be pointing. Internal links will open in the same tab, while external links will open in a new tab.
How determine the number of displayed links
This feature is only available to the for the New layout top bar. You first need to enable it in order to proceed. To enable it just go to the "New layout" section of your admin panel and enable the new top bar for all users. Once you do this you can select the maximum number of links displayed in the top bar. Depending on the number that you select, the rest of the links will be within a dropdown menu next to the displayed links.
How customize the "Post a new listing" button
You can do it by adding a custom message on the section "Post a new listing button text". You need to do this for every language available in your marketplace.
Can I change the order of the displayed links?
You can change the order of the custom links. However, it is not possible at the moment to change the order of the default displayed links or the custom links in relation to the default links.