Hi,
By core things i mean core.js
I have deleted all theme.css and theme.js from template and creating my own.
I do not use webpack, only some prepros tool for sass. I also adding jquery plugins directly to theme via theme config file.... i might build everything with webpack later but as prestashop has its own compression tool inside then i dont see a big difference... all js still will be compresed into one file...
As example, i working right now on checkout. Creating my own ajax to delete or add voucher, update delivery, address forms and many othe stuffs. Mostly for this i would have to change in core.js but instead i just look on github in _core folder how it's done and creating my own based on....
https://github.com/PrestaShop/PrestaShop/tree/develop/themes/_core/js
Basically trying keep everything inside theme as much as possible with default prestashop modules overriden. Touching default controllers override or creating my own only if needed.
Hope that helps. If you have any questions feel free to ask. Happy to help.
Regards