I’ll answer your first question and I highly recommend that you split your questions into multiple threads for a better response by the community.
Since your using Sensible which uses Simple Grid you need to change the columns that are currently assigned to both the content of the page and that of the sidebar.
Simple Grid uses a column format of 12… this means if you have one section 4 columns, the other section would need to be 8… this is because 4+8 = 12. Currently your sidebar uses 3 and the content uses 9… i.e 9+3 = 12… If you want the sidebar bigger then you need to make the content smaller to do so.
You will need to edit single.php and sidebar.php in the root of the Sensible theme folder.
In single.php you need to change:
<div id="primary" class="content-area col-9-12">
to something like: col-8-12
.
Then in sidebar because in the example above we used 8 we now need to use 4.. i.e 8+4 = 12… again. In sidebar.php edit this line:
<div id="secondary" class="widget-area col-3-12" role="complementary">
And use something like col-4-12