First of all don't worry about types of guns and chokes, on your fist visit go along and enjoy yourself sus it out and if you like clay shooting then you can perhaps get yourself an O/U. Most clubs have a friendly bunch of members and will help you along with the safety aspects an how to smoke a clay (not in a pipe but with a shotgun)
Answers to your questions.
1.Pretty much all clay shooters use O/U but there are S/S competitions also
2.Clay competitions are usually restricted to 28gms or 24gm cartridges depending on the discipline with a shot size of no less than a 6
3.A Trap gun is use
