2. How can I reduce the size of my headers h1, h2, h3, h4 etc most especially in the bootstrap3 template?
I did not find a config or style setting which can be adjusted. The only way to change the font-size of headings seems to be to modify the CSS. E.g. if you use the bootswatch theme "flatly" then you need to change the CSS code in the file
lib/tpl/bootstrap3/assets/bootstrap/flatly/bootstrap.min.css
Not very convienient and after an update your changes will be lost! Maybe post a feature-request to the bootstrap3 template maintainer.