I would suggest 45. I've done a 30 minute class, and I felt I could talk more a bit. 60 minutes maybe it's too much, but if you're free and wanna practice more, go ahead, it will sound good for you

It depend or your level and frecuency. More time and frecuency is better.

It depends on your level and your learning goals. I think an hour a week is good for maintaining your level. If you want to improve, you might have to do more, or study a lot outside of lessons. I like to do at least 2 conversation lessons a week in Italian and usually I book 30 minute slots.