Hi,
I am glad that my previous answers were of some help to you.
Regarding the other questions.
1) The view through a flat mirror gives you a true view of what is happening behind you whereas a convex mirror gives the appearance of objects being smaller than they actually are.
2) The exterior mirrors are convex because it gives you a wider field of view.
3) It is not so much the frequency that you should use your mirrors, it is the reason why you are using them. You should look in all your mirrors (including the nearside one) well before you make any movement that will cause you to increase or slow your speed, or to change direction. If you are travelling on a straight road with nothing much happening ( for instance on a Motorway or dual carriageway) then it is advisable to check your mirrors at least once every 10 seconds.
4) Arm signals are not normally used these days unless you want to re-inforce a mechanical signal, or your indicators are not working. In all cases the signal should be given IN GOOD TIME so that other road users can react to what you intend to do.
A point of interest, normally you should not give a signal when moving off from the side of the road, because you should only move off if it is safe to do so, therefore it is no use saying you are moving off if it is not safe to do so.
Hope this helps
Denis