Re: Font-size. I use Charis SIL as my default serif font and have found that converting with Look&Feel - Base font size set to 11pt is just about right for me when I view an EPUB on the PRS-650 on the zoom Medium setting.
Fixing the margins will be different for every EPUB. You need to use calibre's Tweak-EPUB feature to unzip the EPUB and have a look at what's in the .css file. Look for occurrences of
margin-left: and
margin-right: and reduce the attribute values you find. e.g. if you find
margin-left:3em; changing it to
margin-left:0; will remove the left margin. Beware that unless you're familiar with a bit of HTML and CSS this could be assault with a blunt instrument if you change margins for the wrong bit of text. Before you try it the first time, make sure you keep a copy of the pre-tweaked EPUB just in case.
The other place that publishers like to hide ridiculous margins is inside a file called
page-template.xpgt, which only exists in some EPUBs. Poke around inside the EPUB to see if you can find one. You can open it with a text editor. They won't all be exactly the same but here is a short extract from one of mine
Code:
<fo:simple-page-master master-name="single_column" margin-bottom="1.5em" margin-top="1.5em" margin-left="1.5em" margin-right="1.5em" >
<fo:region-body />
</fo:simple-page-master>
If you've got one, again change the margin-left and margin-right settings.
Code:
<fo:simple-page-master master-name="single_column" margin-bottom="1.5em" margin-top="1.5em" margin-left="0em" margin-right="0em" >
<fo:region-body />
</fo:simple-page-master>
I only bother changing the margins in the section named
"single_column"
If all's gone well so far save your changes and press the "Rebuild EPUB" button.
View the EPUB in the Viewer to make sure there have been no obvious mistakes. To the best of my knowledge, the margins from
page-template.xpgt are not visible in the Viewer so you may need to view the EPUB on the PRS650 to be absolutely sure they've gone.