Ok, I know you are getting a lot of different ideas here. I would try the following:
1. delete the css file from the epub/html folder for books already made, otherwise just don't use a css at the sigil step in your workflow. You can even skip the sigil step and simply save your book as clean html in open office for calibre to use.
2. import the book into calibre
3. in calibre's pref screen under conversion, select a bigger base font size. you may have to play with this a bit.
4. use the indent box to insert your indents into your converted epub.
5. use the css box on the conversion prefs screen to add any other css you want.
6. convert the book and try it on your device.
Looking at your css code, most of it will not work very well on the sony device. The sony device can't use the 120% font size very well imo. It only has a limited amount of sizes it produces. IIRC, when the sony looks at the font sizes, it rounds up or down to the size it thinks best fits your css or text based on the font key sizing. You can take a look at
this post if you want to try and sort out some of the complexities of the font key in sony and calibre.