Any cell in a Fusion spreadsheet can be converted to a dropdown using the dropdown and multidropdown functions (e.g. =dropdown(array(1,2,3))). The dropdown function has other optional arguments that can be found in the function library to customize the behavior.
You can lock any set of cells in a shared spreadsheet to prevent accidental edits. Once locked, any user will need to remove the lock to be able to edit the cell again.
The url function allows you to create links in any cell of the spreadsheet. You can use the url_encode and query_params functions to get help formatting a string for a complex URL.