Hello
I can work with you to optimise your site performance through the use of post processing, server configuration, including rewrite, caching, compression and minifying directives and google approved plugin directives. I have extensive experience with Apache and all of its modules and have completed many projects with issues similar to yours, over many years.
If you have not already done so and if you are on a dedicated server, I can install the pagespeed module for you, or if you already have installed it, I can review the directives you currently have and make necessary changes to those.
I can also optimise your Apache installation to run as a high performance server, with specific custom developed Wordpress directives that can speed up your site performance from 30% to 10x the speed on some requests.
I have looked at your htaccess file and can see some issues with it that can be improved, if you would like to send through what version of Apache and Server (OS) you are running, we can start from there and I can develop a plan to implement and optimise the server to ensure it runs at optimal speed for you.
Thank you
Darren
Edit: After reviewing your error log more closely, I can see there is definitely some issues with both your SSL installation and your htaccess file causing server redirect loops, which is most likely the cause of the long time to first byte. I can help you fix those issues.