Hi Daniele... Even if the message is a bit "old", I'll try to give you an answer. I should preface that I have never played the violin myself either... However, my middle school music teacher is a certified violinist, so occasionally he told us something about this instrument.
So. I am almost certain that it is very difficult to learn an instrument like the violin by oneself, which, unfortunately, presents quite a few technical difficulties and more. As you well know, the greatest difficulty in the violin is the fact that on the neck and therefore on its fingerboard there are no "frets", excuse the pun. Let me explain: for example, on a guitar we have metal frets along the neck. In other words, provided the guitar is tuned, we won't have intermediate notes, for example between an A and an A sharp. Just like on the piano.
The violin, however, does not have these frets; therefore, the execution of an "exact" A is not determined by a fret, but by the violinist's skill in "finding" the exact point where the length of the string is such that it produces an A. Obviously, the fact that there are "intermediate notes" is sometimes "exploited", but when it comes to playing exact notes, it becomes rather annoying to hear, for example in a scale, some notes that are slightly flat or slightly sharp. This is the first difficulty.
Secondly, one must take into account that the violin requires a particular preparation, which even I wouldn't know exactly what it is, but which is nonetheless necessary to approach study correctly.
As for purchasing a violin, I wouldn't know how to tell you... In any case, if you want, I will arrange to find out more from my teacher. If you have any particular questions...
See you soon!