A tourist visa is not required for citizens of certain countries for up to 90 days. Please check with the Embassy of Italy in your country if you need or not visa.
Yes. Italy is considered a safe country in general, however as a tourist always be aware of pickpockets and scams in tourist areas.
It is the Euro. You can exchange your dollars upon your arrival or use any ATM machine in Italy, it is very easy.
Italian is the official language in Italy, however, you won’t find problems communicating I English in the most famous touristic places. However, for smaller cities, it is always useful to learn a few sentences that can be a life saviour.
The best time to visit Italy is mid-April to mid-June and mid-September to mid-October when temperatures are pleasant. From July to September it is hotter and more crowded with tourists.
It depends on how much time you have and what you would like to see. To have at least a fine experience that includes most of the main cities 10 days would be recommended.
To travel between cities trains are the best and most affordable option (remember that they departure on time). Pack as light as possible as there is no porters for luggage.
It is better to travel light and to purchase your tickets for major attractions in advance (skip the line passes can be very advantageous to some, such as the Vatican). Always validate your train ticket and do not over tip at bars and restaurants just because you are a tourist.