I cannot answer your question about Italian rating, but I'm nearly sure that your national rating won't go up. They (FIDE and national) are separate rating systems and they shouldn't affect each other.
About the FIDE rating, it is regulated at http://www.fide.com/fide/handbook.html?id=172&view=article
FIDE Rating Regulations effective from 1 July 2014. At article 8.2 you can check the exact formula.
8.2 Determining the Rating 'Ru' in a given event of a previously unrated player.
8.21 If an unrated player scores zero in his first rated event, his score is disregarded.
First determine the average rating of his competition 'Rc'.
(a) In a Swiss or Team tournament: this is simply the average rating of his rated opponents.
(b) The results of both rated and unrated players in a round-robin tournament are taken into account. For unrated players, the average rating of the competition 'Rc' is also the tournament average 'Ra' determined as follows:
(i) Determine the average rating of the rated players 'Rar'.
(ii) Determine p for each of the rated players against all their opponents.
Then determine dp for each of these players.
Then determine the average of these dp = 'dpa'.
(iii) 'n' is the number of opponents.
Ra = Rar - dpa x n/(n+1)
8.22 If he scores 50%, then Ru = Ra
8.23 If he scores more than 50%, then Ru = Ra + 20 for each half point scored over 50%
8.24 If he scores less than 50% in a Swiss or team tournament: Ru = Rc + dp
8.25 If he scores less than 50% in a round-robin: Ru = Ra + dp x n/(n+1).
So, more or less, your initial rating will be your performance in your first tournament(s).