Renting a villa or a house in Italy for the summer is expensive?

No, it's much cheaper than a hotel.

Do you need special documents? Are there any nuances?

No.

And how much time is better to book?

This is a very popular service, good options are booked back in March. The sooner you decide - the better.

And do they also give you an invitation to confirm your visa?

I think yes. When booking such a service, operators receive invitations from partners, not from apartheid owners.

Is it better to do by yourself or through an agency?

As a rule, the operator will give you offers on several coasts, a lot of options. If you do this directly, you will not be able to cover a large number of proposals. This is very laborious.