It depends on what you want to achieve and how deeply you want to explore things. Some people want to work on something very specific for just a session or two. Around 6 - 20 sessions is quite common. And other people may have counselling for years. It's your choice depending on what you want to achieve.
If I have capacity I'll try to arrange your first session within a week, depending on your own availability.
Confidentiality is one of the great benefits of counselling. You can say things to me that you can't say to the people in your life, knowing it'll go no further. But I can't promise 100% confidentiality, because there are some situations where the law requires disclosure. I explain this further in my counselling contract, which you'll see if we work together. But such instances are rare, and would usually only happen after talking to you about it.
I'm afraid not, I only offer 1:1 counselling. I understand that you may want your partner, or a family member of friend to support you, especially in the beginning. But your counselling is for you alone. And in time, you'll see that that's part of what is fantastic about it.