I checked the requirements in the description and screenshots,
For my understanding, you want to convert those checkboxes of categories and brands into a search box, that will show the content when user types and can select an option? (or do you want it to have multiple options selected like a select2 input box which looks like searchbox?).
I understood Point 3. and can be done.
I am well versed with WCFM plugin and can edit the plugin's functionality using either wordpress hooks or editing wcfm template or adding a separate plugin.
I will wait for your response,
Thanks.