Speaking yes, affect your grade. 25% on Speaking, 25% on Listening(P1), 25% on Reading and Directed Writing(P2) and 25% on Continuous writing(P4).

It is not that worrying. It is divided in 3 parts. First,Role Play Card, they are really easy if you practice all the papers from before, they are always repeated .Then, you say the paragraph you prepared at home in French, the Examiner will ask you few questions on the paragraph to make sure you understand what you are saying. Finally, The examiner asks random questions from certain topics, like a country you wish to travel to, food, health,etc...

You won't fail the paper, because you can always guarantee doing well on the first 2 parts, because you usually practice them a lot. Just the 3rd part you MIGHT not understand few questions, doesn't really matter.

Make your paragraph that you prepared at home is long, like 2 minutes and take your time in the Role Play Cards, therefore  you will have less time in the last part so the examiner asks you few questions till the time finishes.

Check this and LEARN them, you will find many of them in the exam :http://www.bbc.co.uk/schools/gcsebitesize/french/

Yes, Its similar to ESL speaking. But in ESL, its just about one "Topic" you talk about and get questions on.

You Welcome. =)