Why does "pound" abbreviates "lbs."

#9 is right. It starts out as a curvilinear E with a cross on the extended base. Crossing a bit of the letter was common to indicate an abbreviation in medieval and modern Latin. per was abbreviated as p with a crossed tail. Recipe ("Take up" or "gather together", the first word in a formula) was abbreviated R with a cross on the extended right leg, still a symbol used for pharmaceutical prescriptions.

On second thought, I think I learned here that it's not so much an abbreviation as a digraph, e and t written as one letter, like a + e -> æ.

#11,
I believe the appropriate term is 'ligature' (as in 'linking') rather than 'digraph'.

I can only speak for U.S. usage, but in my country, the "&" symbol is almost universally used when joining initials. For example, it's AT&T, not AT and T. In Philadelphia, the Department of Licenses and Inspections is L&I, not L and I.

The ampersand is also used in some business names, particularly those consisting of two or more surnames: Smith & Wesson, Johnson & Johnson.