Congratulations to having finished building your alto guitar! I hope it will bring you much pleasure.
I am not an expert on strings, and the selection will depend on the pitch (how high tones you will want). But your choice of ordinary guitar strings for strings number 1 - 6 and number 6 strings (E strings) for strings number 7 - 11 is a good start, and may well be quite suitable.
Strings number 1 - 6 of my alto guitars are 57 cm long, and strings 7 - 11 are gradually longer, just as with your alto guitar. I use for strings 1 - 6 an ordinary set of Savarez Corum Alliance hard tension, and for strings 7 - 11 I use a special Hannabach alto guitar set, which is quite expensive. I think that ordinary #6 (E strings) would do nearly as well for strings 7 - 11.
You can find free scores with both tablature and notes for example at this site: http://www.guitar168.com
This little branle by Jean-Baptiste Besard is short and not too difficult: http://www.guitar168.com/Composers/Besard/Branle/Branle.pdf