Both are registered clinicians, governed by professional bodies. Psychiatrists do a medical degree, then specialise in psychiatric diagnosis and medications, as well as grounding themselves in psychological theory and practices. Psychologists don’t study medicine and are not the best people to ask about issues with medication; that is best left to psychiatrists. However, psychologists do specialise in evidence-based scientific approaches to mental health issues across a broader continuum than is covered in psychiatric training.
This all depends on who is answering the question: they have different training and are registered with different professional bodies, yet in many areas, the work and the tools they use cross over. However, broadly, psychotherapy and counselling focus more on listening. while psychologists tend to interrupt a bit more and offer tools and skills training. That said, this is a massive generalisation and I would say most counsellors and psychotherapists also do what psychologists do to a degree and vice versa. It depends on the therapist as to what modality they work in really; the title is just the training they have received.
There are so many to choose from that this is impossible to answer. Most psychologists have been trained in several techniques and come from an eclectic approach; they will try and use the technique that suits the presentation. I have been trained in numerous approaches however I tend to think CBT is a good starting point, to frame a problem up, in most cases.
This depends on how deep you want to go and how complex the issues are that you are presenting with. Most psychologists will spend the first session getting a good formulation and conceptualisation done – this means a brief history and some basic information – but I try to get down to the thing you came to seek help for, pretty quickly, and fill the missing history bits in later. For most people 4-6 sessions addresses the “here and now” issues satisfactorily. When the issues go a little deeper than that, it can take longer, but not necessarily.