Since you already have the wedding venue arranged, have you been in touch with them to ask for recommendations for local providers? The easiest thing is to go local -- this should keep costs lower than having have someone from further away go to Cortona to provide whatever service you're looking for.
So for catering (and cake), you could try Preludio Catering - http://www.preludiocatering.it/
You need to make sure to request help in getting tables/chairs and all other items as they don't usually provide those directly but work with other companies when they are needed.
For hair, you ccan try Alessandro Fratini - http://www.alessandrofratini.com/
Are you coming over before May to make sure you like the venue and other services being provided?
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