I wont answer all your questions, but I would advise you try to do a flight at least every week when learning. You can maintain fresh momentum, and especially in the uk I would imagine that cancellations due to weather would degrade any less frequent schedule, leaving you quite rusty at the beginning of each lesson. Also, try to look out for an instructor who is a bit older and who also teaches instrument flight. That type of instructor will have the kind of professionalism that you will need to habitually cultivate to be a safe private pilot. Also, have a close look at the quality of the aircraft condition, and the tidiness of the organisations office.
The other main point to make is to never underestimate the importance of your preparation for a flight,and have a keen understanding of the weather, and the state of your judgement when you make decisions in the air. Always build in generous safety margins.