Hi Patrick,
A long time ago I made a Luftwaffe font for this exact purpose. It is based on the DIN 1451 font and made using the Luftwaffe guidelines from WW2. The spacing of the fonts is set up in such a way that it's accurate to specifications, including the Balkenkreuz. Smaller unit characters as used late in the war are possible too. Please see the readme text file included with the font for more information about its use.
http://fonts.skyraider3d.com
This font may be found on other websites too, but it might not be up-to-date there. The original version had a bug (capital X was capital B) which has been fixed in the version on my site.
For RAF, USAAF and other air force fonts, check here:
http://www.simmerspaintshop.com/colours/fonts.html
Regarding your other questions, the fonts can even be used and printed using Word but if you plan on making other markings I recommend using a 2D drawing or image editing program like Illustrator, CorelDraw!, Photoshop, Paint Shop Pro or The Gimp (free).
Scanning depends entirely on your scanner and your ability to adjust colours and contrast afterwards. I wouldn't recommend it. Best scan, then trace using a program like Illustrator or CorelDraw!.