Coilovers And Wheel size

Hii I'm new on here just got my first polo 1.0 mk4 .. Pride and joy :-D

Well so far I've given it a t-cut all round then polished it all up so its gleaming , taken off the bump strips , de-badged it and fitted a bee sting aerial.

Anyways my question is what is the main difference between coilovers and Dampers + springs ? .. I've noticed coilovers seem to be quite a bit cheaper and as I'm on a budget i was thinking of getting them just wanted to know what you guys thaught ?

I'm currently on the stock 13" steelies at the moment but at Christmas I'm hopeing to be getting some 15" alloys but not sure what Tyre yet probably some sort of low profile .. also by what amount do you think i should drop it ? i was thinking 50-60 ? or would this cause the wheels to rub

If anyone can shine any light on this please do i hate my polo being 10 foot in the air

Many thanks