The most important is that you feel free to move: pants, large clothes, socks (anti-sliding are the best), because in relaxation your feet may become cold. You also need a mat - not too soft, not too hard, where you can perform your exercises laying down with comfort and stability. If your mat is too soft you won't be able to work on it standing and feel stability.
No. When you practice the most important is the attention you are paying to your body, to what you are feeling and to the breath. In other words you just need to be focused. Flexibility and tonicity will come with the practice. At the beginning, it is normal to lose concentration. But with the practice the mind becomes trained to stay focused.
No. Usually vegetarianism is associated with yoga practice. But it doesn't have to be so. It all depends on the constitution of each one, his/her activity, the moment in life, etc.
Sometimes it may happen that, as people keep practicing, the interest for certain kinds of food will diminish. You must keep an open mind about this subject and have a lot of discernment before taking radical decisions. When asked, teachers should be able to give good advice about this subject.
No! Each person is different and the way each person performs a posture is unique. You need a teacher to tell you the way how you should execute each pose, so that you don't get hurt and you have all the benefits of the pose.
The way you breath is important too. Your teacher should be able to give you specific directions in this field. These directions vary according to the practitioner.
If you go deeper in the practice of yoga, this aspect is even more relevant!
And if you have questions - and you will - you need a teacher to answer them. You also need a teacher to talk to about how you feel with your practice, your experiences, etc.