I have been using Bootstrap since it was only a bootlace but I use clone template (now V1.2.1) to make a copy and alter only my template version.

I also use separate stylesheets to over ride the original styles to avoid editing the originals eg I have a style sheet named "stylesheet_zcbmh_overides.css" which is loaded after the main "stylesheet.css" to improve on the bootstrap styles that annoy me or to improve the user interface.

I also have style sheets for many of the add-ons I use eg ceon back in stock; securepay; ozpost etc. I also have a style sheet named "stylesheet_xbanner.css" that colours the background on #logowrapper so each of my sites has a different colour and I can look at a screen and immediately determine which environment I am looking at eg vanilla is yellow; test is lime; build is purple; production is red.

Bootstrap 4 v3.2.0 and zc157c work with the followings add-ons: clone template 1.2.1; payment module fee 1-1-0; Direct bank Deposit V1.5.3 (AUS revised); securepayxml (modified for 157c); mod list 1.4.1; ozpost v4.2.7 (modified for 157c); numinix product fields 3.1.2; save your sideboxes layout as the default 151 (mod for 157c); ceon_back_in_stock_notifications V12; export_shipping_information_V1.4; edit_orders-4.6.0; printable price list 3.0.0; missing image checker 2.0 (modified for 157c); sales report 3.4.0; email archive manager 1.9; aupost 2.3;
I hope this helps.

Environment - Production: Zen Cart 157c; Apache 2.4.41; PHP 7.4.3; MySQL 8.0.27; Ubuntu 5.4.0