The letter tool unfortunately doesn’t have the full editing capabilities available for invoices/estimates. Although there is an active feature request to add CSS editing capabilities in the Advanced Customisation tools.
I’ve not tried this but you could add a large white space to the right side of your logo, thus pushing it off to the left. Admittedly it’s a bit of a hack!
The textual content of the footer can be modified in the Letter settings area. The footer also supports some basic HTML markup. Wrapping the text in a <font size='1> tag should work.
You can’t store templated letters as such, you could however just create a base letter and every time you want to reference this just hit the copy button.