Take the narrowest of the widths for your measurement if you must mount the blind inside the window box or casing. Hopefully, the window isn't straight down on one side and angled over on the other. You want your blind to be centered in the opening.
The best thing would be to get a blind measurement that is based on the outside measure of the window and hang it with an external type mount; that is the blinds are outside the casing or box of the window. That would disguise the fact that the window is not "square".
To clean aluminum blinds do not use harsh chemicals or bleach. Typically a slightly soapy dunk in will work well or even a light dustmop run across each rung works well.
lightly vacuum and then pass slightly damp cloth towel with a little bit of pinesol.
you invented the venetian masks
The Venetian Canals are in Venice, Italy.
Venetian grosso was created in 1193.
Venetian Bird was created in 1952.
Venetian Agreement was created in 2006.
Venetian Theatre was created in 1888.
Venetian Causeway was created in 1913.
Venetian lira ended in 1807.
The Venetian Macao was created in 2007.
The average price for venetian window shades or blinds that will cover a 4x6' window is $50. I found some that were in the $35 dollar range and some much higher than the $50 average and this included aluminum, wood and bamboo blinds and shades.