I find violin quite difficult. Maybe its because I never practise it (to the absolute fury of my teacher- you know... inter-instrument jealousy) But I can tell you this, from what I have learned... The first few months are NOT going to be easy. I got frustrated to such a degree when I first started (7), cos it wasnt sounding like what I wanted it to, that I burst into tears and almost threw my violin across the room on numerous occasions. The only thing that stopped me was respect for the instrument itself. Its an exquisite instrument, once you can play it... and the most beautiful sound can be produced, if worked at.
Also, from the very very start, tackle the intonation. There's nothing worse than hearing a string player who's revoltingly out of tune. If you have a good ear this shouldn't be a problem, just concentrate on constantly (and critically) listening to yourself (its very easy for your ear to become accustomed to bad intonation... to the point that you dont even hear it anymore)
Also, find yourself a good teacher (also from the start!). Go on reputation, student success etc
I think its a good idea to have a 2nd instrument, as it gives you a whole lot more musical knowledge and experience, and a different perspective on music as a whole. Also, most undergrad music courses require it for the first few years.
Good luck!
Danyal