So! I have a Rhaetian calendar now.
I rearranged the weeks so that Monday would be the first day of the week and added a week number (à la ISO: week 1 of a year is the first week that contains four days of that calendar year, or equivalently, the first Thursday of the year is in week 1).
Then I had to decide on feasts.
I decided to make Christmas 1 Audunaio, which is 24 December rather than 25, but it seemed like an excuse to say that the (celebration of the) birth of Christ is why the beginning of the year is where it is. That influenced a couple of dates; the circumcision (on the eighth day) and the presentation in the Temple (on the fortieth day) come to mind — oh, and the Annunciation, which I placed on 1 Xanthiko, exactly nine months earlier.
I think I simply translated all the fixed feasts according to common-year calendar equivalences (I picked 2007/2011, which I happened to have handy on my desk).
As for Easter, I decided to put it on the first Sunday on or after 14 Xanthiko.
I think the final tally is: Nativity of the Theotokos (8 September = 15 Gorpiaio); Exaltation of the Cross (14 September = 21 Gorpiaio); Presentation of the Theotokos (21 November = 29 Dio); Nativity of Christ (25 December ~ 1 Audunaio); Baptism-Theophany-Epiphany (6 January ~ 13 Audunaio); Presentation of Christ in the Temple (2 February ~ 9 Peritio); Annunciation (25 March ~ 1 Xanthiko); Palm Sunday (Sunday before Easter: 7-13 Xanthiko); Pascha (Good Friday = 12–18 X., Easter Sunday = 14–20 X., Easter Monday = 15–21 X.); Ascension (40th day after Easter: 23-29 Artemisio); Pentecost–Trinity Sunday (50th day after Easter: 2–8 Daisio) and Monday of the Holy Ghost (51st day after Easter: 3–9 Daisio); Transfiguration (6 August = 12 Loio); Dormition of the Theotokos (15 August = 21 Loio); Peter and Paul (29 June = 5 Panemo); and All Saints (57th day after Easter: 9–15 Daisio).
And, for good measure, the feast day of St. Gall (16 October = 22 Yperberetaio), marked as “National Holiday”.