You can of course experiment with Better WP Security Server Tweaks. We do not troubleshoot or support issues or problems that are caused by other security plugins. You would need to contact that plugin author for help and support for those issues/problems in that plugin.
Everything that is in Better WP Security Server Tweaks is already in BPS standard code and much, much more. In other words, you would be adding redundant code that is less sophisticated and that does not have a built-in method to whitelist things as needed. We have spent a lot of time (years) creating security rules/filters with the built-in capability to whitelist any/all security rules/filters by using the BPS Custom Code feature.
We recommend that you do not use Server Tweaks, but you can of course experiment or make this work by doing whatever is necessary in the Better WP Security plugin's .htaccess code.
If you use the BPS Custom Code feature then you can combine all of your custom or other .htaccess code to create a new custom Master .htaccess file and activate it. See the Custom Code Video Tutorial link on the BPS Custom Code tab page.
See the answer above for your 4th question.