What you'll download is a file that is ready to print straight away, without any need to use booklet format on your printer. Just print this straight to A4 or Letter paper, with duplex set to flip on the short edge (I'd recommend you print just one or two pages first to make sure your printer deals with this correctly and make adjustments as necessary.)
Once you've printed out the pages, you can bind them into a booklet and cut to size using these instructions:
Remember to cut at 130mm (13cm) wide rather than 110mm (11cm) wide as you would for a regular Midori insert.
If there is demand, I'll also make source files available so you can make booklets to cover any period you like and change the fonts and other aspects of the design.
If you've been making your own insert booklets, you'll have a supply of card that you use for the covers. One thing I've been using instead recently is photographic paper. Inspired by the Midori Pan-Am insert, I've found some other vintage airline graphics and made some similar inserts of my own.
These aren't for sale, but just for my own amusement.
Why not find some images that are meaningful for you and use these for your own cover?