You can remove the back and next arrows when you export either by going to in5 > Export HTML5 with in5... or to in5 > Easy Export Wizard... and clicking the Advanced button, going to the Basic section of the Export HTML5 with in5 dialog and deselecting Show Back/Next Arrows.
If you deselect them when you export, you could add your own custom buttons with Go To Previous Page and a Go To Next Page actions.
You could also keep the setting when you export and customize the Back and Next arrows with CSS:
To navigate content, you would need to add either a hyperlink or a button. The default options for hyperlinks and buttons in InDesign and using the in5 Hyperlinks widget (in5 > Interactive Widgets > Hyperlinks) only include options for navigating the current document. They do not include options for navigating from the main layout to embedded content, so you would need to modify the code as described in this comment:
The two ways to modify your exported in5 code are to either use the Resources section or to manually modify the exported code. To modify the code yourself, you open the file that you want to edit in a text editor such as TextEdit (macOS) or Notepad (Windows) or in an IDE such as Dreamweaver which is available if you have the full Adobe Creative Cloud subscription.
If you're not comfortable manually modifying the code, then you may want to reach out to a web developer.