Ideally you could do with going fishing with someone with pole experience (no not that kind [

] ) and have a chance to handle one and see for yourself what you need
generally you get what you pay for and it's better to get a quality 11m pole than a cheap nasty 13m one
As for elastics generally up to size 6 for silvers up to 12 for open water carp and bigger for carp in snaggy swims
I'd stick to ready made rigs such as the preston or maver to start with 0.12 up to 6 elastic, up to 0.16 size 12 elastic and higher for bigger elastics then a pole roller, plummet and your pretty much there with kit you already have [:T]
Everybody has there own ways of fishing pole and advice will differ your own experience will tell you which way to go and I'm sure I've only scratch the surface on what is a highly enjoyable way to fish